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PHENobarbital

Pronunciation

Pronunciation

(fee noe BAR bi tal)

Index Terms

  • Luminal Sodium
  • Phenobarbital Sodium
  • Phenobarbitone
  • Phenylethylmalonylurea

Dosage Forms

Excipient information presented when available (limited, particularly for generics); consult specific product labeling. [DSC] = Discontinued product

Slideshow: View Frightful (But Dead Serious) Drug Side Effects

Elixir, Oral:

Generic: 20 mg/5 mL (5 mL [DSC], 7.5 mL [DSC], 15 mL [DSC], 473 mL)

Solution, Oral:

Generic: 20 mg/5 mL (473 mL)

Solution, Injection, as sodium:

Luminal: 130 mg/mL (1 mL [DSC]) [contains alcohol, usp]

Generic: 65 mg/mL (1 mL); 130 mg/mL (1 mL)

Tablet, Oral:

Generic: 15 mg, 16.2 mg, 30 mg, 32.4 mg, 60 mg, 64.8 mg, 97.2 mg, 100 mg

Brand Names: U.S.

  • Luminal [DSC]

Pharmacologic Category

  • Anticonvulsant, Barbiturate
  • Barbiturate

Pharmacology

Long-acting barbiturate with sedative, hypnotic, and anticonvulsant properties. Barbiturates depress the sensory cortex, decrease motor activity, alter cerebellar function, and produce drowsiness, sedation, and hypnosis. In high doses, barbiturates exhibit anticonvulsant activity; barbiturates produce dose-dependent respiratory depression.

Absorption

Oral: 70% to 90%

Metabolism

Hepatic via hydroxylation and glucuronide conjugation

Excretion

Urine (20% to 50% as unchanged drug)

Onset of Action

Oral: Hypnosis: 20 to 60 minutes; IV: ~5 minutes; Peak effect: IV: ~30 minutes

Time to Peak

Serum: Oral: 1 to 6 hours

Duration of Action

Oral: 6 to 10 hours; IV: 4 to 10 hours

Half-Life Elimination

Neonates: 45 to 500 hours; Infants: 20 to 133 hours; Children: 37 to 73 hours; Adults: 53 to 140 hours

Protein Binding

20% to 45%; decreased in neonates

Use: Labeled Indications

Management of generalized tonic-clonic (grand mal), status epilepticus, and partial seizures; sedative/hypnotic

Note: Use to treat insomnia is not recommended (Schutte-Rodin 2008)

Use: Unlabeled

Sedative/hypnotic withdrawal

Contraindications

Hypersensitivity to barbiturates or any component of the formulation; marked hepatic impairment; dyspnea or airway obstruction; porphyria (manifest and latent); intra-arterial administration, subcutaneous administration (not recommended); use in patients with a history of sedative/hypnotic addiction; nephritic patients (large doses)

Dosage

Sedation:

Children: Oral: 2 mg/kg/dose 3 times daily; maximum dose: 40 mg

Alternative dosing (limited data available): IM, Oral: 2 to 3 mg/kg/day in divided doses every 8 to 12 hours (Nelson 1996)

Adults:

IM, IV: 100 to 320 mg; larger doses may occasionally be necessary in persons with psychoses, and pronounced excitement, and in mental patients with insomnia. The effect of large doses must be closely watched. Maximum: 600 mg daily.

Oral: 30 to 120 mg daily in 2 to 3 divided doses; maximum: 400 mg daily

Status epilepticus: Initial: IV:

Infants, Children, and Adolescents:

American Academy of Pediatrics recommendation: 20 mg/kg (maximum dose: 1,000 mg) over 10 minutes; if necessary, may repeat dose after 15 minutes (maximum total dose: 40 mg/kg) (AAP [Hegenbarth 2008]).

Neurocritical Care Society recommendation: 20 mg/kg (infused at 50 to 100 mg/minute); if necessary, may repeat once after 10 minutes with an additional 5 to 10 mg/kg (NCS [Brophy 2012]).

Manufacturer’s labeling: 15 to 20 mg/kg over 10 to 15 minutes

Adults:

Neurocritical Care Society recommendation: 20 mg/kg (infused at 50 to 100 mg/minute); if necessary, may repeat once after 10 minutes with an additional 5 to 10 mg/kg (NCS [Brophy 2012]).

European Federation of Neurological Societies recommendation: 20 mg/kg (infused at 50 mg/minute); may administer additional boluses in the setting of an ICU. Note: EFNS recommends phenobarbital only for use in refractory complex partial status epilepticus (EFNS [Meierkord 2010]).

Note: Additional respiratory support may be required particularly when maximizing loading dose or if concurrent sedative therapy. Repeat doses administered sooner than 10 to 15 minutes may not allow adequate time for peak CNS concentrations to be achieved and may lead to CNS depression.

Seizures: Maintenance dose:

Manufacturer’s labeling:

Infants, Children, and Adolescents: Oral: 3 to 6 mg/kg/day

Adults: Oral:

Elixir, oral solution: 60 to 200 mg daily

Tablets: 50 to 100 mg 2 or 3 times daily

Alternative dosing (limited data available) (Geurinni 2006; Kliegman 2011):

Initial: Oral, IV:

Infants and Children ≤5 years: 3 to 5 mg/kg/day in 1 to 2 divided doses

Children >5 years: 2 to 3 mg/kg/day in 1 to 2 divided doses

Adolescents: 1 to 3 mg/kg/day in 1 to 2 divided doses (Nelson 1996)

Usual dosing range: Oral, IV: Note: Dosage should be individualized based upon clinical response and serum concentration; once daily doses usually administered at bedtime in children and adolescents. Some centers have used:

Infants: 5 to 6 mg/kg/day in 1 to 2 divided doses

Children:

1 to 5 years: 6 to 8 mg/kg/day in 1 to 2 divided doses

5 to 12 years: 4 to 6 mg/kg/day in 1 to 2 divided doses

Adolescents and Adults: 1 to 3 mg/kg/day in 1 to 2 divided doses or 50 to 100 mg 2 to 3 times daily

Alcohol withdrawal (off-label use):

IV: Initial dose of 260 mg, followed by subsequent doses of 130 mg as needed for symptom control. Note: Clinical Institute Withdrawal Assessment (CIWA) scores were evaluated at 30 minute intervals in the clinical trial (Hendey 2011).

Oral: Fixed dose regimen of 60 mg 4 times daily on day 1, followed by 60 mg 3 times daily on day 2, 60 mg twice daily on day 3, and 30 mg twice daily on day 4. In addition, provide 60 mg as needed for breakthrough withdrawal symptoms (Mariani 2006; Rosenthal 1998). May also administer 130 mg IM as needed for more substantial withdrawal symptoms (eg, heart rate >120 bpm, SBP >150 mm Hg, marked agitation) (Rosenthal 1998).

Sedative/hypnotic withdrawal (off-label use): Oral: Several regimens have been evaluated:

Taper following dosage conversion: Initial daily requirement is determined by substituting phenobarbital in an equivalent dose to the baseline medication (clonazepam 1 mg = phenobarbital 60 mg was used in this study). Divide the calculated baseline total dose into 4 doses and administer every 6 hours for 2 days; then decrease the daily requirement by 10% per day over the next 10 days (Sullivan 1993).

Fixed dose taper: Initial: 200 mg, followed by 100 mg every 4 hours for 5 doses, 60 mg every 4 hours for 4 doses, and then 60 mg every 8 hours for 3 doses (Kawasaki 2012).

Elderly or debilitated: Initiate at the lowest recommended dose.

Dosage adjustment in renal impairment: No specific dosage adjustment provided in manufacturer's labeling; reduced doses are recommended. The following guidelines have been used by some clinicians (Aronoff 2007):

Infants, Children, and Adolescents: Note: Renally adjusted dose recommendations are based on doses of 3 to 7 mg/kg/day every 12 to 24 hours

GFR ≥10 mL/minute/1.73 m2: No dosage adjustment necessary.

GFR <10 mL/minute/1.73 m2: Decrease normal dose by 50% and administer every 24 hours

Intermittent hemodialysis [moderately dialyzable (20% to 50%)]: Supplemental dose may be needed during and after dialysis depending on individual seizure threshold

Peritoneal dialysis (PD): 40% to 50% removed; amount varies depending on number of cycles

Continuous renal replacement therapy (CRRT): Monitor serum concentrations; a case report suggests that clearance and volume of distribution increased with CVVH; more frequent and higher dosing may be necessary in some cases (Pasko 2004)

Adults:

CrCl ≥10 mL/minute: No dosage adjustment necessary.

CrCl <10 mL/minute: Administer every 12 to 16 hours.

Hemodialysis (moderately dialyzable [20% to 50%]): Administer dose before dialysis and 50% of dose after dialysis.

Peritoneal dialysis: Administer 50% of normal dose.

CRRT: Administer normal dose and monitor levels.

Dosage adjustment in hepatic impairment: There are no dosage adjustments provided in manufacturer’s labeling; reduced doses are recommended. Phenobarbital exposure is increased with hepatic impairment; use with caution.

Extemporaneously Prepared

An alcohol-free 10 mg/mL phenobarbital oral suspension may be made from tablets and one of two different vehicles (a 1:1 mixture of Ora-Plus® and Ora-Sweet® or a 1:1 mixture of Ora-Plus® and Ora-Sweet® SF). Crush ten phenobarbital 60 mg tablets in a glass mortar and reduce to a fine powder. Mix 30 mL of Ora-Plus® and 30 mL of either Ora-Sweet® or Ora-Sweet® SF; stir vigorously. Add 15 mL of the vehicle to the powder and mix to a uniform paste. Transfer the mixture to a 2 ounce amber plastic prescription bottle. Rinse mortar and pestle with 15 mL of the vehicle; transfer to bottle. Repeat, then add quantity of vehicle sufficient to make 60 mL. Label "shake well." May mix dose with chocolate syrup (1:1 volume) immediately before administration to mask the bitter aftertaste. Stable for 115 days when stored in amber plastic prescription bottles at room temperature.

Cober M and Johnson CE, “Stability of an Extemporaneously Prepared Alcohol-Free Phenobarbital Suspension,” Am J Health Syst Pharm, 2007, 64(6):644-6.17353574

Administration

May be administered IV, IM or orally.

According to the manufacturer, rapid IV administration >60 mg/minute in adults and >30 mg/minute in children should be avoided. In the setting of status epilepticus, the Neurocritical Care Society and the European Federation of Neurological Societies recommends administration at a rate of 50 to 100 mg/minute (EFNS [Meierkord 2010]; NCS [Brophy 2012]). Avoid extravasation. Intra-arterial injection is contraindicated. Avoid subcutaneous administration.

For IM administration, inject deep into muscle. Do not exceed 5 mL per injection site due to potential for tissue irritation

Dietary Considerations

Vitamin D: Loss in vitamin D due to malabsorption; increase intake of foods rich in vitamin D. Supplementation of vitamin D and/or calcium may be necessary. Injection may contain sodium.

Compatibility

Stable in dextran 6% in dextrose, dextran 6% in NS, D5LR, D51/4NS, D51/2NS, D5NS, D5W, D10W, LR, 1/2NS, NS.

Y-site administration: Incompatible with amphotericin B cholesteryl sulfate complex, pantoprazole.

Compatibility in syringe: Incompatible with hydromorphone, pantoprazole, ranitidine, sufentanil.

Storage

Elixir: Protect from light.

Injection: Protect from light. Not stable in aqueous solutions; use only clear solutions. Do not add to acidic solutions; precipitation may occur.

Drug Interactions

Abiraterone Acetate: CYP3A4 Inducers (Strong) may decrease the serum concentration of Abiraterone Acetate. Management: Avoid whenever possible. If such a combination cannot be avoided, increase abiraterone acetate dosing frequency from once daily to twice daily during concomitant use. Avoid combination

Acetaminophen: Barbiturates may increase the metabolism of Acetaminophen. This may 1) diminish the effect of acetaminophen; and 2) increase the risk of liver damage. Monitor therapy

Afatinib: P-glycoprotein/ABCB1 Inducers may decrease the serum concentration of Afatinib. Management: Per US labeling: if requiring chronic use of P-gp inducers, increase afatinib dose by 10mg as tolerated; reduce to original afatinib dose 2-3 days after stopping P-gp inducers. Per Canadian labeling: avoid combination if possible. Consider therapy modification

Albendazole: PHENobarbital may decrease serum concentrations of the active metabolite(s) of Albendazole. Monitor therapy

Alcohol (Ethyl): CNS Depressants may enhance the CNS depressant effect of Alcohol (Ethyl). Monitor therapy

Amphetamines: May decrease the serum concentration of PHENobarbital. Monitor therapy

Antihepaciviral Combination Products: CYP3A4 Inducers (Strong) may decrease the serum concentration of Antihepaciviral Combination Products. Avoid combination

Apixaban: CYP3A4 Inducers (Strong) may decrease the serum concentration of Apixaban. Avoid combination

Apremilast: CYP3A4 Inducers (Strong) may decrease the serum concentration of Apremilast. Avoid combination

Aprepitant: CYP3A4 Inducers (Strong) may decrease the serum concentration of Aprepitant. Avoid combination

ARIPiprazole: CYP3A4 Inducers may decrease the serum concentration of ARIPiprazole. Management: Double the oral aripiprazole dose and closely monitor response. Reduce oral aripiprazole dose to 10-15 mg/day (for adults) if the inducer is discontinued. Avoid use of CYP3A4 inducers for more than 14 days with extended-release injectable aripiprazole. Consider therapy modification

ARIPiprazole Lauroxil: CYP3A4 Inducers (Strong) may decrease serum concentrations of the active metabolite(s) of ARIPiprazole Lauroxil. Management: Patients taking the 441 mg dose of aripiprazole lauroxil increase their dose to 662 mg if used with a strong CYP3A4 inducer for more than 14 days. No dose adjustment is necessary for patients using the 662 mg or 882 mg doses of aripiprazole lauroxil. Consider therapy modification

Artemether: CYP3A4 Inducers (Strong) may decrease serum concentrations of the active metabolite(s) of Artemether. Specifically, dihydroartemisinin concentrations may be reduced. CYP3A4 Inducers (Strong) may decrease the serum concentration of Artemether. Avoid combination

Axitinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Axitinib. Avoid combination

Azelastine (Nasal): CNS Depressants may enhance the CNS depressant effect of Azelastine (Nasal). Avoid combination

Bazedoxifene: PHENobarbital may decrease the serum concentration of Bazedoxifene. This may lead to loss of efficacy or, if bazedoxifene is combined with estrogen therapy, an increased risk of endometrial hyperplasia. Monitor therapy

Bedaquiline: CYP3A4 Inducers (Strong) may decrease the serum concentration of Bedaquiline. Avoid combination

Bendamustine: CYP1A2 Inducers (Strong) may decrease the serum concentration of Bendamustine. Concentrations of active metabolites may be increased. Monitor therapy

Beta-Blockers: Barbiturates may decrease the serum concentration of Beta-Blockers. Exceptions: Atenolol; Levobunolol; Metipranolol; Nadolol. Monitor therapy

Blood Pressure Lowering Agents: Barbiturates may enhance the hypotensive effect of Blood Pressure Lowering Agents. Monitor therapy

Boceprevir: PHENobarbital may decrease the serum concentration of Boceprevir. Avoid combination

Bortezomib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Bortezomib. Avoid combination

Bosutinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Bosutinib. Avoid combination

Brentuximab Vedotin: CYP3A4 Inducers (Strong) may decrease the serum concentration of Brentuximab Vedotin. Specifically, concentrations of the active monomethyl auristatin E (MMAE) component may be decreased. Monitor therapy

Brentuximab Vedotin: P-glycoprotein/ABCB1 Inducers may decrease the serum concentration of Brentuximab Vedotin. Specifically, concentrations of the active monomethyl auristatin E (MMAE) component may be decreased. Monitor therapy

Brexpiprazole: CYP3A4 Inducers (Strong) may decrease the serum concentration of Brexpiprazole. Management: If brexpiprazole is used together with a strong CYP3A4 inducer, the brexpiprazole dose should gradually be doubled over the course of 1 to 2 weeks. Consider therapy modification

Brimonidine (Topical): May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Buprenorphine: CNS Depressants may enhance the CNS depressant effect of Buprenorphine. Management: Consider reduced doses of other CNS depressants, and avoiding such drugs in patients at high risk of buprenorphine overuse/self-injection. Initiate buprenorphine patches (Butrans brand) at 5 mcg/hr in adults when used with other CNS depressants. Consider therapy modification

Cabozantinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Cabozantinib. Avoid combination

Calcium Channel Blockers: Barbiturates may increase the metabolism of Calcium Channel Blockers. Management: Monitor for decreased therapeutic effects of calcium channel blockers with concomitant barbiturate therapy. Calcium channel blocker dose adjustments may be necessary. Nimodipine Canadian labeling contraindicates concomitant use with phenobarbital. Exceptions: Clevidipine. Monitor therapy

Canagliflozin: PHENobarbital may decrease the serum concentration of Canagliflozin. Management: Consider increasing canagliflozin dose to 300 mg/day in patients with estimated GFR >60 mL/min/1.73 m2 who tolerate canagliflozin 100 mg/day and require greater glycemic control. Consider alternatives in patients with estimated GFR 45-60 mL/min/1.73 m2. Consider therapy modification

Cannabidiol: CYP3A4 Inducers (Strong) may decrease the serum concentration of Cannabidiol. Monitor therapy

Cannabis: CYP3A4 Inducers (Strong) may decrease the serum concentration of Cannabis. More specifically, tetrahydrocannabinol and cannabidiol serum concentrations may be decreased. Monitor therapy

Cannabis: May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Cariprazine: CYP3A4 Inducers (Strong) may decrease the serum concentration of Cariprazine. Avoid combination

Ceritinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Ceritinib. Avoid combination

Chloramphenicol: May decrease the metabolism of Barbiturates. Barbiturates may increase the metabolism of Chloramphenicol. Consider therapy modification

Cholestyramine Resin: May decrease the serum concentration of PHENobarbital. Management: Administer phenobarbital at least 1 hour before or 4-6 hours after administration of cholestyramine in order to minimize the risk for any significant interaction. Consider therapy modification

Clarithromycin: CYP3A4 Inducers (Strong) may increase serum concentrations of the active metabolite(s) of Clarithromycin. Clarithromycin may increase the serum concentration of CYP3A4 Inducers (Strong). CYP3A4 Inducers (Strong) may decrease the serum concentration of Clarithromycin. Management: Consider alternative antimicrobial therapy for patients receiving a CYP3A inducer. Drugs that enhance the metabolism of clarithromycin into 14-hydroxyclarithromycin may alter the clinical activity of clarithromycin and may impair clarithromycin efficacy. Consider therapy modification

CloZAPine: CYP3A4 Inducers (Strong) may decrease the serum concentration of CloZAPine. Avoid combination

CNS Depressants: May enhance the adverse/toxic effect of other CNS Depressants. Exceptions: Levocabastine (Nasal). Monitor therapy

Cobicistat: PHENobarbital may decrease the serum concentration of Cobicistat. Avoid combination

Cobimetinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Cobimetinib. Avoid combination

Contraceptives (Estrogens): Barbiturates may diminish the therapeutic effect of Contraceptives (Estrogens). Contraceptive failure is possible. Management: Use of a non-hormonal contraceptive is recommended. Consider therapy modification

Contraceptives (Progestins): Barbiturates may diminish the therapeutic effect of Contraceptives (Progestins). Contraceptive failure is possible. Management: Use of alternative, nonhormonal contraceptives is recommended. Consider therapy modification

Corticosteroids (Systemic): CYP3A4 Inducers (Strong) may decrease the serum concentration of Corticosteroids (Systemic). Exceptions: Hydrocortisone (Systemic); PrednisoLONE (Systemic); PredniSONE. Monitor therapy

Cosyntropin: May enhance the hepatotoxic effect of PHENobarbital. Monitor therapy

Crizotinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Crizotinib. Avoid combination

Cyclophosphamide: CYP2B6 Inducers (Strong) may increase serum concentrations of the active metabolite(s) of Cyclophosphamide. More specifically, strong CYP2B6 inducers may increase the rate of cyclophosphamide conversion to its primary active metabolite, 4-hydroxycyclophosphamide. Management: Seek alternatives to strong CYP2B6 inducers when possible in patients receiving cyclophosphamide. Monitor patients receiving these combinations closely for evidence of increased cyclophosphamide toxicity. Consider therapy modification

CycloSPORINE (Systemic): Barbiturates may increase the metabolism of CycloSPORINE (Systemic). Consider therapy modification

CYP1A2 Substrates: CYP1A2 Inducers (Strong) may increase the metabolism of CYP1A2 Substrates. Management: Consider an alternative for one of the interacting drugs. Some combinations may be specifically contraindicated. Consult appropriate manufacturer labeling. Consider therapy modification

CYP2A6 Substrates: CYP2A6 Inducers (Strong) may increase the metabolism of CYP2A6 Substrates. Management: Consider an alternative for one of the interacting drugs. Some combinations may be specifically contraindicated. Consult appropriate manufacturer labeling. Consider therapy modification

CYP2B6 Substrates: CYP2B6 Inducers (Strong) may increase the metabolism of CYP2B6 Substrates. Management: Consider an alternative for one of the interacting drugs. Some combinations may be specifically contraindicated. Consult appropriate manufacturer labeling. Consider therapy modification

CYP2C19 Inducers (Strong): May increase the metabolism of CYP2C19 Substrates. Management: Consider an alternative for one of the interacting drugs. Some combinations may be specifically contraindicated. Consult appropriate manufacturer labeling. Consider therapy modification

CYP2C19 Inhibitors (Moderate): May decrease the metabolism of CYP2C19 Substrates. Monitor therapy

CYP2C19 Inhibitors (Strong): May decrease the metabolism of CYP2C19 Substrates. Consider therapy modification

CYP2C8 Substrates: CYP2C8 Inducers (Strong) may increase the metabolism of CYP2C8 Substrates. Management: Consider an alternative for one of the interacting drugs. Some combinations may be specifically contraindicated. Consult appropriate manufacturer labeling. Consider therapy modification

CYP2C9 Substrates: CYP2C9 Inducers (Strong) may increase the metabolism of CYP2C9 Substrates. Management: Consider an alternative for one of the interacting drugs. Some combinations may be specifically contraindicated. Consult appropriate manufacturer labeling. Consider therapy modification

CYP3A4 Substrates: CYP3A4 Inducers (Strong) may increase the metabolism of CYP3A4 Substrates. Management: Consider an alternative for one of the interacting drugs. Some combinations may be specifically contraindicated. Consult appropriate manufacturer labeling. Exceptions: Buprenorphine; Etizolam; Hydrocodone. Consider therapy modification

Dabigatran Etexilate: P-glycoprotein/ABCB1 Inducers may decrease the serum concentration of Dabigatran Etexilate. Management: Avoid concurrent use of dabigatran with p-glycoprotein inducers when possible. Closely monitor for decreased levels/effects of dabigatran if concomitantly administering p-glycoprotein inducers, particularly strong inducers. Avoid combination

Dabrafenib: CYP2C8 Inducers (Strong) may decrease the serum concentration of Dabrafenib. Avoid combination

Dabrafenib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Dabrafenib. Avoid combination

Daclatasvir: CYP3A4 Inducers (Strong) may decrease the serum concentration of Daclatasvir. Avoid combination

Dapsone (Topical): May enhance the adverse/toxic effect of Methemoglobinemia Associated Agents. Monitor therapy

Darunavir: May decrease the serum concentration of PHENobarbital. Monitor therapy

Dasatinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Dasatinib. Management: Avoid when possible. If such a combination cannot be avoided, consider increasing dasatinib dose and monitor clinical response and toxicity closely. Consider therapy modification

Deferasirox: PHENobarbital may decrease the serum concentration of Deferasirox. Management: Avoid combination when possible; if the combination must be used, consider a 50% increase in initial deferasirox dose, with monitoring of serum ferritin concentrations and clinical responses to guide further dosing. Consider therapy modification

Dexamethasone (Systemic): CYP3A4 Inducers (Strong) may decrease the serum concentration of Dexamethasone (Systemic). Management: Consider dexamethasone dose increases in patients receiving strong CYP3A4 inducers and monitor closely for reduced steroid efficacy. Consider therapy modification

Dexmethylphenidate: May increase the serum concentration of PHENobarbital. Monitor therapy

Diclofenac (Systemic): CYP2C9 Inducers (Strong) may decrease the serum concentration of Diclofenac (Systemic). Monitor therapy

Dienogest: CYP3A4 Inducers (Strong) may decrease the serum concentration of Dienogest. Management: Avoid use of dienogest for contraception when using medications that induce CYP3A4 and for at least 28 days after discontinuation of a CYP3A4 inducer. An alternative form of contraception should be used during this time. Avoid combination

Disopyramide: PHENobarbital may decrease the serum concentration of Disopyramide. Monitor therapy

Dolutegravir: PHENobarbital may decrease the serum concentration of Dolutegravir. Avoid combination

DOXOrubicin (Conventional): CYP3A4 Inducers (Strong) may decrease the serum concentration of DOXOrubicin (Conventional). Management: Seek alternatives to strong CYP3A4 inducers in patients treated with doxorubicin. One U.S. manufacturer (Pfizer Inc.) recommends that these combinations be avoided. Consider therapy modification

DOXOrubicin (Conventional): P-glycoprotein/ABCB1 Inducers may decrease the serum concentration of DOXOrubicin (Conventional). Management: Seek alternatives to P-glycoprotein inducers in patients treated with doxorubicin whenever possible. One U.S. manufacturer (Pfizer Inc.) recommends that these combinations be avoided. Consider therapy modification

Doxycycline: Barbiturates may decrease the serum concentration of Doxycycline. Consider therapy modification

Doxylamine: May enhance the CNS depressant effect of CNS Depressants. Management: The manufacturer of Diclegis (doxylamine/pyridoxine), intended for use in pregnancy, specifically states that use with other CNS depressants is not recommended. Monitor therapy

Dronabinol: CYP3A4 Inducers (Strong) may decrease the serum concentration of Dronabinol. Monitor therapy

Dronabinol: May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Dronedarone: CYP3A4 Inducers (Strong) may decrease the serum concentration of Dronedarone. Avoid combination

Droperidol: May enhance the CNS depressant effect of CNS Depressants. Management: Consider dose reductions of droperidol or of other CNS agents (e.g., opioids, barbiturates) with concomitant use. Consider therapy modification

Eliglustat: CYP3A4 Inducers (Strong) may decrease the serum concentration of Eliglustat. Avoid combination

Elvitegravir: PHENobarbital may decrease the serum concentration of Elvitegravir. Avoid combination

Enzalutamide: CYP2C8 Inducers (Strong) may decrease the serum concentration of Enzalutamide. Avoid combination

Enzalutamide: CYP3A4 Inducers (Strong) may decrease the serum concentration of Enzalutamide. Management: Consider using an alternative agent that has no or minimal CYP3A4 induction potential when possible. If this combination cannot be avoided, increase the dose of enzalutamide from 160 mg daily to 240 mg daily. Avoid combination

Erlotinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Erlotinib. Management: Avoid combination if possible. If combination must be used, increase erlotinib dose by 50 mg increments every 2 weeks as tolerated, to a maximum of 450 mg/day. Consider therapy modification

Eslicarbazepine: PHENobarbital may decrease the serum concentration of Eslicarbazepine. Monitor therapy

Etizolam: CYP3A4 Inducers (Strong) may decrease the serum concentration of Etizolam. Monitor therapy

Etoposide: CYP3A4 Inducers (Strong) may decrease the serum concentration of Etoposide. Management: When possible, seek alternatives to strong CYP3A4-inducing medications in patients receiving etoposide. If these combinations cannot be avoided, monitor patients closely for diminished etoposide response. Consider therapy modification

Etoposide Phosphate: CYP3A4 Inducers (Strong) may decrease the serum concentration of Etoposide Phosphate. Management: When possible, seek alternatives to strong CYP3A4-inducing medications in patients receiving etoposide phosphate. If these combinations cannot be avoided, monitor patients closely for diminished etoposide phosphate response. Consider therapy modification

Etravirine: PHENobarbital may decrease the serum concentration of Etravirine. Avoid combination

Everolimus: CYP3A4 Inducers (Strong) may decrease the serum concentration of Everolimus. Management: Avoid concurrent use of strong CYP3A4 inducers, but if strong CYP3A4 inducers cannot be avoided, consider gradually (in 5 mg increments) increasing the everolimus dose from 10 mg/day to 20 mg/day (adult doses). Avoid combination

Exemestane: CYP3A4 Inducers (Strong) may decrease the serum concentration of Exemestane. Management: Exemestane U.S. product labeling recommends using an increased dose (50 mg/day) in patients receiving concurrent strong CYP3A4 inducers. The Canadian product labeling does not recommend a dose adjustment with concurrent use of strong CYP3A4 inducers. Consider therapy modification

Felbamate: PHENobarbital may decrease the serum concentration of Felbamate. Felbamate may increase the serum concentration of PHENobarbital. Management: In patients receiving phenobarbital, initiate felbamate at 1200 mg/day in divided doses 3-4 times daily and reduce phenobarbital dose by 20%. Monitor for increased phenobarbital concentrations/effects and decreased felbamate concentrations/effects. Consider therapy modification

FentaNYL: CYP3A4 Inducers (Strong) may decrease the serum concentration of FentaNYL. Monitor therapy

Flibanserin: CYP3A4 Inducers (Strong) may decrease the serum concentration of Flibanserin. Avoid combination

Folic Acid: May decrease the serum concentration of PHENobarbital. Monitor therapy

Fosphenytoin: May enhance the CNS depressant effect of PHENobarbital. Fosphenytoin may increase the serum concentration of PHENobarbital. PHENobarbital may decrease the serum concentration of Fosphenytoin. Monitor therapy

Gefitinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Gefitinib. Management: In the absence of severe adverse reactions, increase gefitinib dose to 500 mg daily in patients receiving strong CYP3A4 inducers; resume 250 mg dose 7 days after discontinuation of the strong inducer. Carefully monitor clinical response. Consider therapy modification

Griseofulvin: Barbiturates may decrease the serum concentration of Griseofulvin. Monitor therapy

GuanFACINE: CYP3A4 Inducers (Strong) may decrease the serum concentration of GuanFACINE. Management: Consider increasing the guanfacine dose by 2-fold when adding a strong CYP3A4 inducer. Titrate the guanfacine dose up to a max of 8 mg/day when starting guanfacine in a patient who is taking a strong CYP3A4 inhibitor. Consider therapy modification

Hemin: Barbiturates may diminish the therapeutic effect of Hemin. Avoid combination

Hydrocodone: CNS Depressants may enhance the CNS depressant effect of Hydrocodone. Management: Consider starting with a 20% to 30% lower hydrocodone dose when using together with any other CNS depressant. Dose reductions in the other CNS depressant may also be warranted. Consider therapy modification

Hydrocortisone (Systemic): CYP3A4 Inducers (Strong) may decrease the serum concentration of Hydrocortisone (Systemic). Monitor therapy

HydrOXYzine: May enhance the CNS depressant effect of Barbiturates. Management: Consider a decrease in the barbiturate dose, as appropriate, when used together with hydroxyzine. With concurrent use, monitor patients closely for excessive response to the combination. Consider therapy modification

Ibrutinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Ibrutinib. Avoid combination

Idelalisib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Idelalisib. Avoid combination

Imatinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Imatinib. Management: Avoid concurrent use of imatinib with strong CYP3A4 inducers when possible. If such a combination must be used, increase imatinib dose by at least 50% and monitor the patient's clinical response closely. Consider therapy modification

Irinotecan Products: CYP3A4 Inducers (Strong) may decrease serum concentrations of the active metabolite(s) of Irinotecan Products. Specifically, serum concentrations of SN-38 may be reduced. CYP3A4 Inducers (Strong) may decrease the serum concentration of Irinotecan Products. Avoid combination

Isavuconazonium Sulfate: CYP3A4 Inducers (Strong) may decrease serum concentrations of the active metabolite(s) of Isavuconazonium Sulfate. Specifically, CYP3A4 Inducers (Strong) may decrease isavuconazole serum concentrations. Avoid combination

Itraconazole: CYP3A4 Inducers (Strong) may decrease the serum concentration of Itraconazole. Avoid combination

Ivabradine: CYP3A4 Inducers (Strong) may decrease the serum concentration of Ivabradine. Avoid combination

Ivacaftor: CYP3A4 Inducers (Strong) may decrease the serum concentration of Ivacaftor. Avoid combination

Ixabepilone: CYP3A4 Inducers (Strong) may decrease the serum concentration of Ixabepilone. Management: Avoid this combination whenever possible. If this combination must be used, a gradual increase in ixabepilone dose from 40 mg/m2 to 60 mg/m2 (given as a 4-hour infusion), as tolerated, should be considered. Consider therapy modification

Ixazomib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Ixazomib. Avoid combination

Kava Kava: May enhance the adverse/toxic effect of CNS Depressants. Monitor therapy

Lacosamide: PHENobarbital may decrease the serum concentration of Lacosamide. Monitor therapy

LamoTRIgine: Barbiturates may decrease the serum concentration of LamoTRIgine. Management: See lamotrigine prescribing information for specific age-dependent dosing guidelines regarding concurrent use with a barbiturate, as well as for adjusting lamotrigine dosing if concurrent barbiturate therapy is discontinued. Consider therapy modification

Lapatinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Lapatinib. Management: If therapy overlap cannot be avoided, consider titrating lapatinib gradually from 1,250 mg/day up to 4,500 mg/day (HER2 positive metastatic breast cancer) or 1,500 mg/day up to 5,500 mg/day (hormone receptor/HER2 positive breast cancer) as tolerated. Avoid combination

Ledipasvir: P-glycoprotein/ABCB1 Inducers may decrease the serum concentration of Ledipasvir. Avoid combination

Leucovorin Calcium-Levoleucovorin: May decrease the serum concentration of PHENobarbital. Monitor therapy

Levomefolate: May decrease the serum concentration of PHENobarbital. Monitor therapy

Linagliptin: CYP3A4 Inducers (Strong) may decrease the serum concentration of Linagliptin. Management: Strongly consider using an alternative to any strong CYP3A4 inducer in patients who are being treated with linagliptin. If this combination is used, monitor patients closely for evidence of reduced linagliptin effectiveness. Consider therapy modification

Linagliptin: P-glycoprotein/ABCB1 Inducers may decrease the serum concentration of Linagliptin. Management: Strongly consider using an alternative to any strong P-glycoprotein inducer in patients who are being treated with linagliptin. If this combination is used, monitor patients closely for evidence of reduced linagliptin effectiveness. Consider therapy modification

Lopinavir: PHENobarbital may decrease the serum concentration of Lopinavir. Management: Increased doses of lopinavir may be necessary when using these agents in combination. Do not use a once daily lopinavir/ritonavir regimen together with phenobarbital. Increase monitoring of therapeutic response in all patients using this combination. Consider therapy modification

Luliconazole: May increase the serum concentration of CYP2C19 Substrates. Monitor therapy

Lumacaftor: May decrease the serum concentration of CYP2C19 Substrates. Monitor therapy

Lumefantrine: CYP3A4 Inducers (Strong) may decrease the serum concentration of Lumefantrine. Avoid combination

Lurasidone: CYP3A4 Inducers (Strong) may decrease the serum concentration of Lurasidone. Avoid combination

Macitentan: CYP3A4 Inducers (Strong) may decrease the serum concentration of Macitentan. Avoid combination

Magnesium Sulfate: May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Maraviroc: CYP3A4 Inducers (Strong) may decrease the serum concentration of Maraviroc. Management: Increase maraviroc adult dose to 600 mg twice daily when used with strong CYP3A4 inducers. This does not apply to patients also receiving strong CYP3A4 inhibitors. Do not use maraviroc with strong CYP3A4 inducers in patients with CrCl less than 30 mL/min. Consider therapy modification

Mefloquine: May diminish the therapeutic effect of Anticonvulsants. Mefloquine may decrease the serum concentration of Anticonvulsants. Management: Mefloquine is contraindicated for malaria prophylaxis in persons with a history of convulsions. Monitor anticonvulsant concentrations and treatment response closely with concurrent use. Consider therapy modification

Meperidine: Barbiturates may enhance the CNS depressant effect of Meperidine. Barbiturates may increase serum concentrations of the active metabolite(s) of Meperidine. Monitor therapy

Methadone: PHENobarbital may decrease the serum concentration of Methadone. Monitor therapy

Methotrimeprazine: CNS Depressants may enhance the CNS depressant effect of Methotrimeprazine. Methotrimeprazine may enhance the CNS depressant effect of CNS Depressants. Management: Reduce adult dose of CNS depressant agents by 50% with initiation of concomitant methotrimeprazine therapy. Further CNS depressant dosage adjustments should be initiated only after clinically effective methotrimeprazine dose is established. Consider therapy modification

Methylfolate: May decrease the serum concentration of PHENobarbital. Monitor therapy

Methylphenidate: May increase the serum concentration of PHENobarbital. Monitor therapy

MethylPREDNISolone: CYP3A4 Inducers (Strong) may decrease the serum concentration of MethylPREDNISolone. Management: Consider methylprednisolone dose increases in patients receiving strong CYP3A4 inducers and monitor closely for reduced steroid efficacy. Consider therapy modification

MetroNIDAZOLE (Systemic): PHENobarbital may decrease the serum concentration of MetroNIDAZOLE (Systemic). Monitor therapy

Metyrosine: CNS Depressants may enhance the sedative effect of Metyrosine. Monitor therapy

Mianserin: May enhance the CNS depressant effect of Barbiturates. Mianserin may diminish the therapeutic effect of Barbiturates. Barbiturates may decrease the serum concentration of Mianserin. Avoid combination

Mifepristone: CYP3A4 Inducers (Strong) may decrease the serum concentration of Mifepristone. Avoid combination

Minocycline: May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Multivitamins/Minerals (with ADEK, Folate, Iron): May decrease the serum concentration of Barbiturates. Monitor therapy

Nabilone: May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Naloxegol: CYP3A4 Inducers (Strong) may decrease the serum concentration of Naloxegol. Avoid combination

Netupitant: CYP3A4 Inducers (Strong) may decrease the serum concentration of Netupitant. Avoid combination

NIFEdipine: CYP3A4 Inducers (Strong) may decrease the serum concentration of NIFEdipine. Avoid combination

Nilotinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Nilotinib. Avoid combination

NiMODipine: CYP3A4 Inducers (Strong) may decrease the serum concentration of NiMODipine. Avoid combination

Nintedanib: Combined Inducers of CYP3A4 and P-glycoprotein may decrease the serum concentration of Nintedanib. Avoid combination

Nisoldipine: CYP3A4 Inducers (Strong) may decrease the serum concentration of Nisoldipine. Avoid combination

Nitric Oxide: May enhance the adverse/toxic effect of Methemoglobinemia Associated Agents. Combinations of these agents may increase the likelihood of significant methemoglobinemia. Management: Monitor patients for signs of methemoglobinemia (e.g., hypoxia, cyanosis) when nitric oxide is used in combination with other agents associated with development of methemoglobinemia. Avoid lidocaine/prilocaine. Monitor therapy

Olaparib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Olaparib. Avoid combination

Ombitasvir, Paritaprevir, Ritonavir, and Dasabuvir: CYP2C8 Inducers (Strong) may decrease the serum concentration of Ombitasvir, Paritaprevir, Ritonavir, and Dasabuvir. Specifically, the serum concentrations of dasabuvir may decrease significantly. Avoid combination

Orlistat: May decrease the serum concentration of Anticonvulsants. Monitor therapy

Orphenadrine: CNS Depressants may enhance the CNS depressant effect of Orphenadrine. Avoid combination

Osimertinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Osimertinib. Avoid combination

OXcarbazepine: PHENobarbital may decrease serum concentrations of the active metabolite(s) of OXcarbazepine. Specifically, concentrations of the major active 10-monohydroxy metabolite may be reduced. OXcarbazepine may increase the serum concentration of PHENobarbital. Management: Consider increasing the initial adult oxcarbazepine extended release tablet (Oxtellar XR) dose to 900 mg/day. No specific recommendations are available for other oxcarbazepine formulations. Consider therapy modification

Palbociclib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Palbociclib. Avoid combination

Paliperidone: Inducers of CYP3A4 (Strong) and P-glycoprotein may decrease the serum concentration of Paliperidone. Management: Avoid using the 3-month extended-release injectable suspension (Invega Trinza) with inducers of both CYP3A4 and P-glycoprotein during the 3-month dosing interval if possible. If combination is necessary, consider using extended-release tablets. Consider therapy modification

Panobinostat: CYP3A4 Inducers (Strong) may decrease the serum concentration of Panobinostat. Avoid combination

Paraldehyde: CNS Depressants may enhance the CNS depressant effect of Paraldehyde. Avoid combination

PAZOPanib: CYP3A4 Inducers (Strong) may decrease the serum concentration of PAZOPanib. Avoid combination

Perampanel: CYP3A4 Inducers (Strong) may decrease the serum concentration of Perampanel. Management: Avoid use of perampanel with strong CYP3A inducers other than enzyme-inducing antiepileptic drugs (EIAEDs). Increase perampanel starting dose to 4 mg/day when used with EIAEDs such as phenytoin, carbamazepine, or oxcarbazepine. Avoid combination

P-glycoprotein/ABCB1 Substrates: P-glycoprotein/ABCB1 Inducers may decrease the serum concentration of P-glycoprotein/ABCB1 Substrates. P-glycoprotein inducers may also further limit the distribution of p-glycoprotein substrates to specific cells/tissues/organs where p-glycoprotein is present in large amounts (e.g., brain, T-lymphocytes, testes, etc.). Monitor therapy

Phenytoin: May enhance the CNS depressant effect of PHENobarbital. PHENobarbital may decrease the serum concentration of Phenytoin. Phenytoin may increase the serum concentration of PHENobarbital. Monitor therapy

Pirfenidone: CYP1A2 Inducers (Strong) may decrease the serum concentration of Pirfenidone. Avoid combination

PONATinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of PONATinib. Avoid combination

Pramipexole: CNS Depressants may enhance the sedative effect of Pramipexole. Monitor therapy

Praziquantel: CYP3A4 Inducers (Strong) may decrease the serum concentration of Praziquantel. Management: Avoid concomitant use of praziquantel with strong CYP3A4 inducers. Discontinue rifampin 4 weeks prior to initiation of praziquantel therapy. Rifampin may be resumed the day following praziquantel completion. Avoid combination

PrednisoLONE (Systemic): CYP3A4 Inducers (Strong) may decrease the serum concentration of PrednisoLONE (Systemic). Monitor therapy

PredniSONE: CYP3A4 Inducers (Strong) may decrease the serum concentration of PredniSONE. Monitor therapy

Prilocaine: Methemoglobinemia Associated Agents may enhance the adverse/toxic effect of Prilocaine. Combinations of these agents may increase the likelihood of significant methemoglobinemia. Management: Monitor patients for signs of methemoglobinemia (e.g., hypoxia, cyanosis) when prilocaine is used in combination with other agents associated with development of methemoglobinemia. Avoid lidocaine/prilocaine in infants receiving such agents. Monitor therapy

Primidone: May enhance the adverse/toxic effect of Barbiturates. Primidone is converted to phenobarbital, and thus becomes additive with existing barbiturate therapy. Monitor therapy

Propacetamol: Barbiturates may increase the metabolism of Propacetamol. This may 1) diminish the desired effects of propacetamol; and 2) increase the risk of liver damage. Monitor therapy

Propafenone: CYP3A4 Inducers (Strong) may decrease the serum concentration of Propafenone. Monitor therapy

Pyridoxine: May increase the metabolism of Barbiturates. Apparent in high pyridoxine doses (eg, 200 mg/day) Monitor therapy

QUEtiapine: CYP3A4 Inducers (Strong) may decrease the serum concentration of QUEtiapine. Management: Quetiapine dose increases to as much as 5 times the regular dose may be required to maintain therapeutic benefit. Reduce the quetiapine dose back to the previous/regular dose within 7-14 days of discontinuing the inducer. Consider therapy modification

QuiNIDine: PHENobarbital may enhance the hepatotoxic effect of QuiNIDine. PHENobarbital may decrease the serum concentration of QuiNIDine. Monitor therapy

QuiNINE: May increase the serum concentration of PHENobarbital. PHENobarbital may decrease the serum concentration of QuiNINE. Consider therapy modification

Ranolazine: CYP3A4 Inducers (Strong) may decrease the serum concentration of Ranolazine. Avoid combination

Regorafenib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Regorafenib. Avoid combination

Rifamycin Derivatives: May increase the metabolism of Barbiturates. Monitor therapy

Rilpivirine: PHENobarbital may decrease the serum concentration of Rilpivirine. Avoid combination

Rivaroxaban: CYP3A4 Inducers (Strong) may decrease the serum concentration of Rivaroxaban. Avoid combination

Roflumilast: CYP3A4 Inducers (Strong) may decrease the serum concentration of Roflumilast. Management: Roflumilast U.S. prescribing information recommends against combining strong CYP3A4 inducers with roflumilast. The Canadian product monograph makes no such recommendation but notes that such agents may reduce roflumilast therapeutic effects. Avoid combination

Rolapitant: CYP3A4 Inducers (Strong) may decrease the serum concentration of Rolapitant. Management: Avoid rolapitant use in patients requiring chronic administration of strong CYP3A4 inducers. Monitor for reduced rolapitant response and the need for alternative or additional antiemetic therapy even with shorter-term use of such inducers. Consider therapy modification

RomiDEPsin: CYP3A4 Inducers (Strong) may decrease the serum concentration of RomiDEPsin. Avoid combination

Rotigotine: CNS Depressants may enhance the sedative effect of Rotigotine. Monitor therapy

Rufinamide: May increase the serum concentration of PHENobarbital. PHENobarbital may decrease the serum concentration of Rufinamide. Monitor therapy

Saxagliptin: CYP3A4 Inducers may decrease the serum concentration of Saxagliptin. Monitor therapy

Selective Serotonin Reuptake Inhibitors: CNS Depressants may enhance the adverse/toxic effect of Selective Serotonin Reuptake Inhibitors. Specifically, the risk of psychomotor impairment may be enhanced. Monitor therapy

Simeprevir: CYP3A4 Inducers (Strong) may decrease the serum concentration of Simeprevir. Avoid combination

Sodium Nitrite: Methemoglobinemia Associated Agents may enhance the adverse/toxic effect of Sodium Nitrite. Combinations of these agents may increase the likelihood of significant methemoglobinemia. Monitor therapy

Sodium Oxybate: May enhance the CNS depressant effect of CNS Depressants. Management: Consider alternatives to combined use. When combined use is needed, consider minimizing doses of one or more drugs. Use of sodium oxybate with alcohol or sedative hypnotics is contraindicated. Consider therapy modification

Sofosbuvir: P-glycoprotein/ABCB1 Inducers may decrease the serum concentration of Sofosbuvir. Avoid combination

Somatostatin Acetate: May enhance the adverse/toxic effect of Barbiturates. Specifically, Somatostatin Acetate may enhance or prolong Barbiturate effects, including sedative effects. Avoid combination

Sonidegib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Sonidegib. Avoid combination

SORAfenib: CYP3A4 Inducers (Strong) may decrease the serum concentration of SORAfenib. Avoid combination

Stiripentol: PHENobarbital may decrease the serum concentration of Stiripentol. Avoid combination

SUNItinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of SUNItinib. Management: Avoid when possible. If such a combination cannot be avoided, consider increasing sunitinib dose and monitor clinical response and toxicity closely. Consider therapy modification

Suvorexant: CYP3A4 Inducers (Strong) may decrease the serum concentration of Suvorexant. Avoid combination

Tadalafil: CYP3A4 Inducers (Strong) may decrease the serum concentration of Tadalafil. Management: Erectile dysfunction: monitor for decreased effectiveness - no standard dose adjustments recommended. Avoid use of tadalafil for pulmonary arterial hypertension in patients receiving a strong CYP3A4 inducer. Consider therapy modification

Tapentadol: May enhance the CNS depressant effect of CNS Depressants. Management: Start tapentadol at a dose of one-third to one-half of the normal dose if being initiated in a patient who is taking another drug with CNS depressant effects. Monitor closely for evidence of excessive CNS depression. Consider therapy modification

Tasimelteon: CYP3A4 Inducers (Strong) may decrease the serum concentration of Tasimelteon. Avoid combination

Telaprevir: PHENobarbital may decrease the serum concentration of Telaprevir. Avoid combination

Teniposide: Barbiturates may decrease the serum concentration of Teniposide. Management: Consider alternatives to combined treatment with barbiturates and teniposide due to the potential for decreased teniposide concentrations. If the combination cannot be avoided, monitor teniposide response closely. Consider therapy modification

Tetrahydrocannabinol: CYP3A4 Inducers (Strong) may decrease the serum concentration of Tetrahydrocannabinol. Monitor therapy

Tetrahydrocannabinol: May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Thalidomide: CNS Depressants may enhance the CNS depressant effect of Thalidomide. Avoid combination

Thiazide Diuretics: Barbiturates may enhance the orthostatic hypotensive effect of Thiazide Diuretics. Monitor therapy

Ticagrelor: CYP3A4 Inducers (Strong) may decrease serum concentrations of the active metabolite(s) of Ticagrelor. CYP3A4 Inducers (Strong) may decrease the serum concentration of Ticagrelor. Avoid combination

Tipranavir: PHENobarbital may decrease the serum concentration of Tipranavir. Tipranavir may decrease the serum concentration of PHENobarbital. Consider therapy modification

Tofacitinib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Tofacitinib. Avoid combination

Tolvaptan: CYP3A4 Inducers (Strong) may decrease the serum concentration of Tolvaptan. Management: If concurrent use is necessary, increased doses of tolvaptan (with close monitoring for toxicity and clinical response) may be needed. Avoid combination

Toremifene: CYP3A4 Inducers (Strong) may decrease the serum concentration of Toremifene. Avoid combination

Trabectedin: CYP3A4 Inducers (Strong) may decrease the serum concentration of Trabectedin. Avoid combination

Treprostinil: CYP2C8 Inducers (Strong) may decrease the serum concentration of Treprostinil. Monitor therapy

Tricyclic Antidepressants: Barbiturates may increase the metabolism of Tricyclic Antidepressants. Consider therapy modification

Ulipristal: CYP3A4 Inducers (Strong) may decrease the serum concentration of Ulipristal. Avoid combination

Ulipristal: Barbiturates may decrease the serum concentration of Ulipristal. Avoid combination

Valproate Products: May increase the serum concentration of Barbiturates. Barbiturates may decrease the serum concentration of Valproate Products. Monitor therapy

Vandetanib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Vandetanib. Avoid combination

Vemurafenib: CYP3A4 Inducers (Strong) may decrease the serum concentration of Vemurafenib. Avoid combination

Vilazodone: CYP3A4 Inducers (Strong) may decrease the serum concentration of Vilazodone. Management: Consider increasing vilazodone dose by as much as 2-fold (do not exceed 80 mg/day), based on response, in patients receiving strong CYP3A4 inducers for > 14 days. Reduce to the original vilazodone dose over 1-2 weeks after inducer discontinuation. Consider therapy modification

VinCRIStine (Liposomal): CYP3A4 Inducers (Strong) may decrease the serum concentration of VinCRIStine (Liposomal). Avoid combination

VinCRIStine (Liposomal): P-glycoprotein/ABCB1 Inducers may decrease the serum concentration of VinCRIStine (Liposomal). Avoid combination

Vitamin K Antagonists (eg, warfarin): Barbiturates may increase the metabolism of Vitamin K Antagonists. Consider therapy modification

Vorapaxar: CYP3A4 Inducers (Strong) may decrease the serum concentration of Vorapaxar. Avoid combination

Voriconazole: Barbiturates may decrease the serum concentration of Voriconazole. Avoid combination

Vortioxetine: CYP3A4 Inducers (Strong) may decrease the serum concentration of Vortioxetine. Management: Consider increasing the vortioxetine dose to no more than 3 times the original dose when used with a strong drug metabolism inducer for more than 14 days. The vortioxetine dose should be returned to normal within 14 days of stopping the strong inducer. Consider therapy modification

Zaleplon: CYP3A4 Inducers (Strong) may decrease the serum concentration of Zaleplon. Management: Consider the use of an alternative hypnotic that is not metabolized by CYP3A4 in patients receiving strong CYP3A4 inducers. If zalephon is combined with a strong CYP3A4 inducer, monitor for decreased effectiveness of zaleplon. Consider therapy modification

Zolpidem: CNS Depressants may enhance the CNS depressant effect of Zolpidem. Management: Reduce the Intermezzo brand sublingual zolpidem adult dose to 1.75 mg for men who are also receiving other CNS depressants. No such dose change is recommended for women. Avoid use with other CNS depressants at bedtime; avoid use with alcohol. Consider therapy modification

Zonisamide: PHENobarbital may decrease the serum concentration of Zonisamide. Monitor therapy

Zuclopenthixol: CYP3A4 Inducers (Strong) may decrease the serum concentration of Zuclopenthixol. Monitor therapy

Test Interactions

Assay interference of LDH

Adverse Reactions

Frequency not defined.

Cardiovascular: Bradycardia, hypotension, syncope

Central nervous system: Agitation, anxiety, ataxia, CNS excitation or depression, confusion, dizziness drowsiness, hallucinations, “hangover” effect, headache, hyperkinesia, impaired judgment, insomnia, lethargy, nervousness, nightmares, somnolence

Dermatologic: Exfoliative dermatitis, rash, Stevens-Johnson syndrome

Gastrointestinal: Nausea, vomiting, constipation

Hematologic: Agranulocytosis, thrombocytopenia, megaloblastic anemia

Local: Pain at injection site, thrombophlebitis with IV use

Renal: Oliguria

Respiratory: Laryngospasm, respiratory depression, apnea (especially with rapid IV use), hypoventilation

Miscellaneous: Gangrene with inadvertent intra-arterial injection

Warnings/Precautions

Concern related to adverse effects:

• CNS depression: May cause CNS depression, which may impair physical or mental abilities; patients must be cautioned about performing tasks which require mental alertness (eg, operating machinery or driving).

• Hypotension: May cause hypotension particularly when administered intravenously; use with caution in hemodynamically unstable patients (hypotension or shock).

• Paradoxical stimulatory response: May cause paradoxical responses, including agitation and hyperactivity, particularly in acute pain and pediatric patients.

• Respiratory depression: May cause respiratory depression particularly when administered intravenously; use with caution patients with respiratory disease.

Disease-related concerns:

• Depression: Use with caution in patients with depression or suicidal tendencies.

• Hepatic impairment: Use with caution in patients with hepatic impairment.

• Hypoadrenalism: Use with caution in patients with hypoadrenalism.

• Renal impairment: Use with caution in patients with renal impairment.

• Substance abuse: Use with caution in patients with a history of drug abuse; potential for drug dependency exists. Tolerance, psychological and physical dependence may occur with prolonged use.

Concurrent drug therapy issues:

• Sedatives: Effects with other sedative drugs or ethanol may be potentiated.

Special populations:

• Debilitated patients: Use with caution in patients who are debilitated.

• Elderly: Avoid use due to risk of overdose with low dosages, tolerance to sleep effects, and increased risk of physical dependence (Beers Criteria).

• Pediatric: Phenobarbital has been associated with cognitive deficits in children receiving chronic therapy for febrile seizures.

Dosage form specific issues:

• Injection: Intra-arterial administration may cause reactions ranging from transient pain to gangrene and is contraindicated. Subcutaneous administration may cause tissue irritation (eg, redness, tenderness, necrosis) and is not recommended.

• Propylene glycol: Some dosage forms may contain propylene glycol; large amounts are potentially toxic and have been associated hyperosmolality, lactic acidosis, seizures and respiratory depression; use caution (AAP 1997; Zar 2007).

Other warnings/precautions:

• Acute pain: Do not administer to patients in acute pain.

• Withdrawal: Anticonvulsants should not be discontinued abruptly because of the possibility of increasing seizure frequency; therapy should be withdrawn gradually to minimize the potential of increased seizure frequency, unless safety concerns require a more rapid withdrawal.

Monitoring Parameters

Phenobarbital serum concentrations, mental status, CBC, LFTs, seizure activity

Pregnancy Risk Factor

B/D (manufacturer dependent)

Pregnancy Considerations

Barbiturates can be detected in the placenta, fetal liver, and fetal brain. Fetal and maternal blood concentrations may be similar following parenteral administration. An increased incidence of fetal abnormalities may occur following maternal use. The use of folic acid throughout pregnancy and vitamin K during the last month of pregnancy is recommended; epilepsy itself, number of medications, genetic factors, or a combination of these probably influence the teratogenicity of anticonvulsant therapy. When used during the third trimester of pregnancy, withdrawal symptoms may occur in the neonate, including seizures and hyperirritability; symptoms of withdrawal may be delayed in the neonate up to 14 days after birth. Use during labor does not impair uterine activity; however, respiratory depression may occur in the newborn; resuscitation equipment should be available, especially for premature infants.

Patient Education

• Discuss specific use of drug and side effects with patient as it relates to treatment. (HCAHPS: During this hospital stay, were you given any medicine that you had not taken before? Before giving you any new medicine, how often did hospital staff tell you what the medicine was for? How often did hospital staff describe possible side effects in a way you could understand?)

• Patient may experience fatigue, headache, nausea, or injection site irritation. Have patient report immediately to prescriber dyspnea, severe dizziness, syncope, bradycardia, significant change in balance, illogical thinking, considerable anxiety, intolerable asthenia, osteodynia, Stevens-Johnson syndrome/toxic epidermal necrolysis, or insomnia (HCAHPS).

• Educate patient about signs of a significant reaction (eg, wheezing; chest tightness; fever; itching; bad cough; blue skin color; seizures; or swelling of face, lips, tongue, or throat). Note: This is not a comprehensive list of all side effects. Patient should consult prescriber for additional questions.

Intended Use and Disclaimer: Should not be printed and given to patients. This information is intended to serve as a concise initial reference for health care professionals to use when discussing medications with a patient. You must ultimately rely on your own discretion, experience, and judgment in diagnosing, treating, and advising patients.

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