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Cimetidine

Pronunciation

Pronunciation

(sye MET i deen)

Dosage Forms

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

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Solution, Oral, as hydrochloride [strength expressed as base]:

Generic: 300 mg/5 mL (237 mL, 240 mL, 473 mL [DSC])

Tablet, Oral:

Cimetidine Acid Reducer: 200 mg

Heartburn Relief: 200 mg [DSC] [contains polysorbate 80]

Tagamet HB: 200 mg

Generic: 200 mg, 300 mg, 400 mg, 800 mg

Brand Names: U.S.

  • Cimetidine Acid Reducer [OTC]
  • Heartburn Relief [OTC] [DSC]
  • Tagamet HB [OTC]

Pharmacologic Category

  • Histamine H2 Antagonist

Pharmacology

Competitive inhibition of histamine at H2 receptors of the gastric parietal cells resulting in reduced gastric acid secretion, gastric volume and hydrogen ion concentration reduced

Absorption

Rapid

Distribution

1 to 1.5 L/kg (Somogyi 1983)

Metabolism

Partially hepatic, forms metabolites (Somogyi 1983)

Excretion

Primarily urine (48% as unchanged drug); feces (2%) (Somogyi 1983)

Onset of Action

1 hour

Time to Peak

Serum: Oral: 0.75 to 1.5 hours

Duration of Action

80% reduction in gastric acid secretion for 4 to 5 hours after 300 mg dose

Half-Life Elimination

Neonates: 3.6 hours; Children: 1.4 hours; Adults: ~2 hours

Protein Binding

20% (Somogyi 1983)

Special Populations: Renal Function Impairment

Drug accumulation may occur in patients with severe renal failure.

Use: Labeled Indications

Duodenal ulcer: Short-term treatment of active duodenal ulcer and maintenance therapy after the healing of active ulcer.

Gastric ulcer: Short-term treatment of active, benign gastric ulcer.

Gastroesophageal reflux disease: Treatment of erosive gastroesophageal reflux disease (GERD).

Pathological hypersecretory conditions: Treatment of pathological hypersecretory conditions (eg, Zollinger-Ellison syndrome, systemic mastocytosis, multiple endocrine adenomas).

Heartburn (OTC only): Relief and prevention of heartburn associated with acid indigestion and sour stomach.

Use: Unlabeled

Part of a multidrug regimen for H. pylori eradication to reduce the risk of duodenal ulcer recurrence

Contraindications

Hypersensitivity to cimetidine or any component of the formulation

OTC labeling: When used for self-medication (OTC), do not use if trouble or pain when swallowing food, vomiting with blood, or bloody or black stools, allergic to cimetidine or other acid reducers. Do not use with other acid reducers.

Documentation of allergenic cross-reactivity for histamine H2 antagonists is limited. However, because of similarities in chemical structure and/or pharmacologic actions, the possibility of cross-sensitivity cannot be ruled out with certainty.

Dosage

Oral:

Children and Adolescents <16 years: 20 to 40 mg/kg/day (limited experience)

Children ≥12 years, Adolescents, and Adults: Heartburn (OTC labeling):

Prevention: 200 mg daily up to 30 minutes prior to eating foods or beverages that cause heartburn (maximum: 400 mg/24 hours).

Relief of symptoms: 200 mg daily; maximum: 400 mg/24 hours.

Adults:

Duodenal ulcer, active: 300 mg 4 times daily or 800 mg at bedtime or 400 mg twice daily for up to 8 weeks

Note: Higher doses of 1600 mg at bedtime for 4 weeks may be beneficial for a subpopulation of patients with larger duodenal ulcers (>1 cm defined endoscopically) who are also heavy smokers (≥1 pack/day).

Duodenal ulcer, prophylaxis: 400 mg at bedtime

Gastric ulcer, active: 300 mg 4 times daily or 800 mg at bedtime for up to 8 weeks

Gastroesophageal reflux disease: 400 mg 4 times daily or 800 mg twice daily for 12 weeks

Pathological hypersecretory conditions: 300 mg 4 times daily; adjust dose to patient response; maximum 2.4 g/day

Helicobacter pylori eradication (off-label use): 400 mg twice daily; requires combination therapy with antibiotics

Interstitial cystitis (bladder pain syndrome) (off-label use): 600 to 800 mg daily in divided doses as 200 mg 3 times daily or as 300 to 400 mg twice daily (Dasgupta 2001; Seshadri 1994; Thilagarajah 2001)

Dosage adjustment in renal impairment:

Manufacturer’s labeling:

Mild to moderate renal impairment: There are no dosage adjustments provided in the manufacturer’s labeling; use with caution.

Severe renal impairment: 300 mg every 12 hours; may increase frequency with caution. When hepatic impairment is also present, further reductions in dosage may be necessary.

Alternate recommendations (Aronoff 2007):

GFR >50 mL/minute: No dosage adjustment necessary.

GFR 10 to 50 mL/minute: Administer 50% of normal dose

GFR <10 mL/minute: 300 mg every 8 to 12 hours

Hemodialysis: Dose after dialysis

CCRT: Administer 50% of normal dose

Peritoneal dialysis: 300 mg every 8 to 12 hours

Dosage adjustment in hepatic impairment: There are no dosage adjustments provided in the manufacturer’s labeling; use with caution. Dosage adjustments may be needed in patients with both renal and hepatic impairment.

Extemporaneously Prepared

Note: Commercial oral solution is available (strength expressed as base: 60 mg/mL)

A 60 mg/mL oral suspension may be made with tablets. Place twenty-four 300 mg tablets in 5 mL of sterile water for ~3-5 minutes to dissolve film coating. Crush tablets in a mortar and reduce to a fine powder. Add 10 mL of glycerin and mix to a uniform paste; mix while adding Simple Syrup, NF in incremental proportions to almost 120 mL; transfer to a calibrated bottle, rinse mortar with vehicle, and add quantity of vehicle sufficient to make 120 mL. Label "shake well" and "refrigerate". Stable for 17 days.

Nahata MC, Pai VB, and Hipple TF, Pediatric Drug Formulations, 5th ed, Cincinnati, OH: Harvey Whitney Books Co, 2004.

Administration

Administer with meals.

Storage

Store at room temperature. Protect from light.

Drug Interactions

Alfentanil: Cimetidine may increase the serum concentration of Alfentanil. Monitor therapy

Amiodarone: Cimetidine may increase the serum concentration of Amiodarone. Management: Consider alternatives to cimetidine. If this combination cannot be avoided, monitor for increased amiodarone concentrations/effects with cimetidine initiation/dose increase or decreased concentrations/effects with cimetidine discontinuation/dose decrease. Consider therapy modification

ARIPiprazole: CYP3A4 Inhibitors (Weak) may increase the serum concentration of ARIPiprazole. Management: Monitor for increased aripiprazole pharmacologic effects. Aripiprazole dose adjustments may or may not be required based on concomitant therapy and/or indication. Consult full interaction monograph for specific recommendations. Monitor therapy

ARIPiprazole: CYP2D6 Inhibitors (Moderate) may increase the serum concentration of ARIPiprazole. Management: Monitor for increased aripiprazole pharmacologic effects. Aripiprazole dose adjustments may or may not be required based on concomitant therapy and/or indication. Consult full interaction monograph for specific recommendations. Monitor therapy

Atazanavir: H2-Antagonists may decrease the serum concentration of Atazanavir. Management: Specific dose limitations and administration guidelines exist; consult full interaction monograph or atazanavir prescribing information. Consider therapy modification

AtorvaSTATin: May enhance the adverse/toxic effect of Cimetidine. Specifically, there is a theoretical potential for enhanced effects on reducing endogenous steroid activity. Monitor therapy

Bosutinib: H2-Antagonists may decrease the serum concentration of Bosutinib. Management: Administer histamine H2 receptor antagonists more than 2 hours before or after bosutinib. Consider therapy modification

Brexpiprazole: CYP2D6 Inhibitors (Moderate) may increase the serum concentration of Brexpiprazole. Management: If brexpiprazole is to be used together with both a moderate CYP2D6 inhibitor and a strong or moderate CYP3A4 inhibitor, the brexpiprazole dose should be reduced to 25% of the usual dose. Monitor therapy

Bromazepam: Cimetidine may increase the serum concentration of Bromazepam. Management: Consider use of bromazepam with an H2-antagonist that is not a potent CYP inhibitor (e.g., ranitidine) or alternatively, consider use of cimetidine with a benzodiazepine that does not undergo oxidative metabolism (e.g., lorazepam). Consider therapy modification

BuPROPion: May increase the serum concentration of OCT2 Substrates. Monitor therapy

Calcium Channel Blockers: Cimetidine may increase the serum concentration of Calcium Channel Blockers. Management: Consider alternatives to cimetidine. If no suitable alternative exists, monitor for increased effects of calcium channel blockers following cimetidine initiation/dose increase, and decreased effects following cimetidine discontinuation/dose decrease. Exceptions: AmLODIPine; Clevidipine; NiCARdipine. Consider therapy modification

Capecitabine: Cimetidine may increase serum concentrations of the active metabolite(s) of Capecitabine. Specifically, concentrations of fluorouracil may be increased. Monitor therapy

CarBAMazepine: Cimetidine may increase the serum concentration of CarBAMazepine. The serum carbamazepine concentration might return to normal within one week of starting cimetidine. Monitor therapy

Carmustine: Cimetidine may enhance the myelosuppressive effect of Carmustine. Management: Consider alternatives to cimetidine in patients receiving carmustine. If the combination cannot be avoided, monitor for enhanced carmustine myelotoxicity. Consider therapy modification

Carvedilol: Cimetidine may increase the serum concentration of Carvedilol. Monitor therapy

Cefditoren: H2-Antagonists may decrease the serum concentration of Cefditoren. Management: Concomitant use of cefditoren with H2-antagonists and antacids is not recommended. Consider alternative methods to control acid reflux (eg, diet modification) or alternative antimicrobial therapy if use of H2-antagonists can not be avoided. Consider therapy modification

Cefpodoxime: H2-Antagonists may decrease the absorption of Cefpodoxime. Separate oral doses by at least 2 hours. Monitor therapy

Cefuroxime: H2-Antagonists may decrease the absorption of Cefuroxime. Separate oral doses by at least 2 hours. Monitor therapy

Cilostazol: CYP2C19 Inhibitors may increase the serum concentration of Cilostazol. Management: Consider reducing the cilostazol dose to 50 mg twice daily in patients who are also receiving inhibitors of CYP2C19. Consider therapy modification

Cisapride: Cimetidine may increase the serum concentration of Cisapride. Management: Consider alternatives to cimetidine. If this combination cannot be avoided, monitor for toxic effects of cisapride if cimetidine is initiated/dose increased, or decreased efficacy if cimetidine is discontinued/dose decreased. Consider therapy modification

Citalopram: CYP2C19 Inhibitors (Moderate) may increase the serum concentration of Citalopram. Management: Limit citalopram dose to a maximum of 20 mg/day if used with a moderate CYP2C19 inhibitor. Patients using this combination should be monitored closely for evidence of citalopram toxicity (e.g., serotonin syndrome, QT prolongation, etc.). Consider therapy modification

Clopidogrel: CYP2C19 Inhibitors (Moderate) may decrease serum concentrations of the active metabolite(s) of Clopidogrel. Management: Due to a risk for impaired clopidogrel effectiveness with such a combination, carefully consider the need for a moderate CYP2C19 inhibitor in patients receiving clopidogrel. Monitor patients closely for evidence of a diminished response to clopidogrel. Consider therapy modification

CloZAPine: Cimetidine may increase the serum concentration of CloZAPine. Management: Consider use of an alternative H2 antagonist. Monitor for increased toxic effects of clozapine if cimetidine is initiated/dose increased, or decreased effects if cimetidine is discontinued/dose decreased. Consider therapy modification

Codeine: CYP2D6 Inhibitors (Moderate) may diminish the therapeutic effect of Codeine. These CYP2D6 inhibitors may prevent the metabolic conversion of codeine to its active metabolite morphine. Monitor therapy

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

CYP2D6 Substrates: CYP2D6 Inhibitors (Moderate) may decrease the metabolism of CYP2D6 Substrates. Exceptions: Tamoxifen. Monitor therapy

Cysteamine (Systemic): H2-Antagonists may diminish the therapeutic effect of Cysteamine (Systemic). Monitor therapy

Dabrafenib: H2-Antagonists may decrease the serum concentration of Dabrafenib. Monitor therapy

Dalfampridine: Cimetidine may increase the serum concentration of Dalfampridine. Management: Recommendations differ significantly between international labelings in regards to the concomitant use of dalfampridine (referred to as fampridine in Canada) and cimetidine. Consult appropriate product labeling. Monitor therapy

Dasatinib: H2-Antagonists may decrease the absorption of Dasatinib. Management: Antacids (taken 2 hours before or after dasatinib administration) can be used in place of H2-antagonists if some acid-reducing therapy is needed. Avoid combination

Delavirdine: H2-Antagonists may decrease the serum concentration of Delavirdine. Management: Chronic therapy with H2-antagonists should be avoided in patients who are being treated with delavirdine. The clinical significance of short-term H2-antagonist therapy with delavirdine is uncertain, but such therapy should be undertaken with caution. Avoid combination

Dexmethylphenidate: H2-Antagonists may increase the absorption of Dexmethylphenidate. Specifically, H2-antagonists may interfere with the normal release of drug from the extended-release capsules (Focalin XR brand), which could result in both increased absorption (early) and decreased delayed absorption. Monitor therapy

Dofetilide: Cimetidine may increase the serum concentration of Dofetilide. This is likely via inhibition of dofetilide renal tubular secretion (primarily) and inhibition of dofetilide metabolism. Avoid combination

Doxofylline: Cimetidine may increase the serum concentration of Doxofylline. Monitor therapy

DOXOrubicin (Conventional): CYP2D6 Inhibitors (Moderate) may increase the serum concentration of DOXOrubicin (Conventional). Management: Seek alternatives to moderate CYP2D6 inhibitors in patients treated with doxorubicin whenever possible. One U.S. manufacturer (Pfizer Inc.) recommends that these combinations be avoided. Consider therapy modification

Eliglustat: CYP2D6 Inhibitors (Moderate) may increase the serum concentration of Eliglustat. Management: Reduce the eliglustat dose to 84 mg daily. Avoid use of eliglustat in combination with a moderate CYP2D6 inhibitor and a strong or moderate CYP3A4 inhibitor. Consider therapy modification

EPIrubicin: Cimetidine may increase the serum concentration of EPIrubicin. Avoid combination

Erlotinib: H2-Antagonists may decrease the serum concentration of Erlotinib. Management: Avoid H2-antagonists in patients receiving erlotinib when possible. If concomitant treatment cannot be avoided, erlotinib should be dosed once daily, 10 hours after and at least 2 hours before H2-antagonist dosing. Consider therapy modification

Escitalopram: Cimetidine may increase the serum concentration of Escitalopram. Management: Consider using an alternative H2-antagonist to avoid the risk of escitalopram toxicity. Escitalopram Canadian product labeling recommends limiting escitalopram dose to 10 mg/day with concomitant use of cimetidine. Consider therapy modification

Fesoterodine: CYP2D6 Inhibitors may increase serum concentrations of the active metabolite(s) of Fesoterodine. Monitor therapy

Flibanserin: CYP3A4 Inhibitors (Weak) may increase the serum concentration of Flibanserin. Monitor therapy

Floxuridine: Cimetidine may increase serum concentrations of the active metabolite(s) of Floxuridine. Specifically, concentrations of fluorouracil may be increased. Monitor therapy

Fluorouracil (Systemic): Cimetidine may increase the serum concentration of Fluorouracil (Systemic). Monitor therapy

Fosamprenavir: H2-Antagonists may decrease the serum concentration of Fosamprenavir. Cimetidine may also inhibit the metabolism of the active metabolite amprenavir, making its effects on fosamprenavir/amprenavir concentrations difficult to predict. Monitor therapy

Fosphenytoin-Phenytoin: Cimetidine may enhance the adverse/toxic effect of Fosphenytoin-Phenytoin. Cimetidine may increase the serum concentration of Fosphenytoin-Phenytoin. Management: Consider using an alternative H2-antagonist to avoid this interaction. Monitor for toxic effects of hydantoin anticonvulsants if cimetidine is initiated/dose increased. Consider therapy modification

Gefitinib: H2-Antagonists may decrease the serum concentration of Gefitinib. Management: Administer gefitinib at least 6 hours before or after administration of a histamine H2-antagonist, and closely monitor clinical response to gefitinib. Consider therapy modification

Hydrocodone: CYP3A4 Inhibitors (Weak) may increase the serum concentration of Hydrocodone. Monitor therapy

Indinavir: H2-Antagonists may decrease the serum concentration of Indinavir. Monitor therapy

Iron Salts: H2-Antagonists may decrease the absorption of Iron Salts. Exceptions: Ferric Carboxymaltose; Ferric Citrate; Ferric Gluconate; Ferric Pyrophosphate Citrate; Ferumoxytol; Iron Dextran Complex; Iron Sucrose. Monitor therapy

Itraconazole: H2-Antagonists may decrease the serum concentration of Itraconazole. Management: When this combination is used, the itraconazole should be administered with a cola beverage (8 ounces). Itraconazole oral suspension may be less sensitive to this interaction. Monitor patient response to itraconazole closely. Consider therapy modification

Ketoconazole (Systemic): H2-Antagonists may decrease the serum concentration of Ketoconazole (Systemic). Management: Administer oral ketoconazole at least 2 hours prior to use of any H2-receptor antagonist. Monitor patients closely for signs of inadequate clinical response to ketoconazole. Consider therapy modification

Ledipasvir: H2-Antagonists may decrease the serum concentration of Ledipasvir. Consider therapy modification

Lomitapide: CYP3A4 Inhibitors (Weak) may increase the serum concentration of Lomitapide. Management: Limit the maximum adult dose of lomitapide to 30 mg daily when used in combination with any weak CYP3A4 inhibitor. Consider therapy modification

Lumacaftor: May decrease the serum concentration of P-glycoprotein/ABCB1 Substrates. Lumacaftor may increase the serum concentration of P-glycoprotein/ABCB1 Substrates. Monitor therapy

Mebendazole: Cimetidine may increase the serum concentration of Mebendazole. Monitor therapy

Meperidine: Cimetidine may increase the serum concentration of Meperidine. Monitor therapy

Mesalamine: H2-Antagonists may diminish the therapeutic effect of Mesalamine. Histamine H2-Antagonist-mediated increases in gastrointestinal pH may cause the premature release of mesalamine from specific sustained-release mesalamine products. Management: Consider avoiding concurrent administration of high-dose histamine H2-receptor antagonists with sustained-release mesalamine products. Consider therapy modification

MetFORMIN: Cimetidine may increase the serum concentration of MetFORMIN. Consider therapy modification

Methylphenidate: H2-Antagonists may increase the absorption of Methylphenidate. Specifically, H2-antagonists may interfere with the normal release of drug from the extended-release capsules (Ritalin LA brand), which could result in both increased absorption (early) and decreased delayed absorption. Monitor therapy

Metoprolol: CYP2D6 Inhibitors may increase the serum concentration of Metoprolol. Management: Consider an alternative for one of the interacting drugs in order to avoid metoprolol toxicity. If the combination must be used, monitor response to metoprolol closely. Metoprolol dose reductions may be necessary. Consider therapy modification

Moclobemide: Cimetidine may decrease the metabolism of Moclobemide. Management: Consider using alternative agents to lower gastric pH in order to avoid this interaction. If combined, a moclobemide dose reduction of 50% is recommended and patients should be monitored for increased moclobemide effects/toxicities. Consider therapy modification

Multivitamins/Minerals (with ADEK, Folate, Iron): H2-Antagonists may decrease the serum concentration of Multivitamins/Minerals (with ADEK, Folate, Iron). Specifically, the absorption of iron may be impaired by H2-antagonists. Monitor therapy

Nebivolol: CYP2D6 Inhibitors (Moderate) may increase the serum concentration of Nebivolol. Monitor therapy

Nelfinavir: H2-Antagonists may decrease the serum concentration of Nelfinavir. Concentrations of the active M8 metabolite may also be reduced. Monitor therapy

Nicotine: Cimetidine may increase the serum concentration of Nicotine. Monitor therapy

Nilotinib: H2-Antagonists may decrease the serum concentration of Nilotinib. Management: The nilotinib dose should be given 10 hours after or 2 hours before the H2 receptor antagonist in order to minimize the risk of a significant interaction. Consider therapy modification

PAZOPanib: H2-Antagonists may decrease the serum concentration of PAZOPanib. Management: Avoid the use of histamine H2-antagonists in combination with pazopanib. Strategies to minimize the expected interaction between these agents (eg, dose separation) have not been investigated. Avoid combination

Pentoxifylline: Cimetidine may increase the serum concentration of Pentoxifylline. Monitor therapy

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

P-glycoprotein/ABCB1 Inhibitors: May increase the serum concentration of P-glycoprotein/ABCB1 Substrates. P-glycoprotein inhibitors may also enhance 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

Pimozide: CYP3A4 Inhibitors (Weak) may increase the serum concentration of Pimozide. Avoid combination

Posaconazole: H2-Antagonists may decrease the serum concentration of Posaconazole. Management: Avoid concurrent use of oral suspension with H2-antagonists whenever possible. Monitor patients closely for decreased antifungal effects if this combination is used. Delayed-release posaconazole tablets may be less likely to interact. Consider therapy modification

Pramipexole: Cimetidine may increase the serum concentration of Pramipexole. Monitor therapy

Praziquantel: Cimetidine may increase the serum concentration of Praziquantel. Monitor therapy

Procainamide: Cimetidine may increase the serum concentration of Procainamide. Management: Consider an alternative H2-receptor antagonist in patients taking procainamide. If combined, monitor for increased therapeutic effects/toxicity of procainamide. Consider therapy modification

Propafenone: Cimetidine may increase the serum concentration of Propafenone. Monitor therapy

QuiNIDine: Cimetidine may increase the serum concentration of QuiNIDine. Management: Consider alternatives to cimetidine. If the combination cannot be avoided, monitor for increased quinidine concentrations/toxicity with cimetidine initiation/dose increase, or decreased concentrations/effects with cimetidine discontinuation/dose decrease. Consider therapy modification

QuiNINE: Cimetidine may increase the serum concentration of QuiNINE. Consider therapy modification

Ranolazine: May increase the serum concentration of P-glycoprotein/ABCB1 Substrates. Monitor therapy

Rilpivirine: H2-Antagonists may decrease the serum concentration of Rilpivirine. Management: Administer histamine H2 receptor antagonists at least 12 hours before or 4 hours after rilpivirine. Consider therapy modification

Risedronate: H2-Antagonists may increase the serum concentration of Risedronate. This applies specifically to delayed-release risedronate. Avoid combination

Roflumilast: Cimetidine may increase serum concentrations of the active metabolite(s) of Roflumilast. Cimetidine may increase the serum concentration of Roflumilast. Monitor therapy

Saquinavir: H2-Antagonists may increase the serum concentration of Saquinavir. Monitor therapy

Selective Serotonin Reuptake Inhibitors: Cimetidine may decrease the metabolism of Selective Serotonin Reuptake Inhibitors. Consider therapy modification

Sulfonylureas: Cimetidine may increase the serum concentration of Sulfonylureas. Monitor therapy

Tamoxifen: CYP2D6 Inhibitors (Moderate) may decrease serum concentrations of the active metabolite(s) of Tamoxifen. Specifically, CYP2D6 inhibitors may decrease the metabolic formation of highly potent active metabolites. Management: Consider alternatives with less of an inhibitory effect on CYP2D6 activity when possible. Consider therapy modification

Tamsulosin: Cimetidine may increase the serum concentration of Tamsulosin. Monitor therapy

Tegafur: Cimetidine may increase serum concentrations of the active metabolite(s) of Tegafur. Specifically, concentrations of fluorouracil may be increased. Monitor therapy

Teriflunomide: May increase the serum concentration of OAT3 Substrates. Monitor therapy

Theophylline Derivatives: Cimetidine may decrease the metabolism of Theophylline Derivatives. Exceptions: Dyphylline. Consider therapy modification

Thioridazine: CYP2D6 Inhibitors may increase the serum concentration of Thioridazine. Avoid combination

TiZANidine: CYP1A2 Inhibitors (Weak) may increase the serum concentration of TiZANidine. Management: Avoid these combinations when possible. If combined use cannot be avoided, initiate tizanidine at an adult dose of 2 mg and increase in 2-4 mg increments based on patient response. Monitor for increased effects of tizanidine, including adverse reactions. Consider therapy modification

TraMADol: CYP2D6 Inhibitors (Moderate) may diminish the therapeutic effect of TraMADol. These CYP2D6 inhibitors may prevent the metabolic conversion of tramadol to its active metabolite that accounts for much of its opioid-like effects. Monitor therapy

Tricyclic Antidepressants: Cimetidine may decrease the metabolism of Tricyclic Antidepressants. Monitor therapy

Varenicline: H2-Antagonists may increase the serum concentration of Varenicline. Management: Monitor for increased varenicline adverse effects with concomitant use of cimetidine or other H2-antagonists, particularly in patients with severe renal impairment. International product labeling recommendations vary. Consult appropriate labeling. Monitor therapy

Vitamin K Antagonists (eg, warfarin): Cimetidine may enhance the anticoagulant effect of Vitamin K Antagonists. Consider therapy modification

Zaleplon: Cimetidine may decrease the metabolism of Zaleplon. Consider therapy modification

ZOLMitriptan: Cimetidine may increase the serum concentration of ZOLMitriptan. Monitor therapy

Adverse Reactions

1% to 10%:

Central nervous system: Headache (2% to 4%), dizziness (1%), drowsiness (1%), agitation

Endocrine & metabolic: Gynecomastia (<1% to 4%)

Gastrointestinal: Diarrhea (1%)

Frequency not defined:

Cardiovascular: Atrioventricular block, bradycardia, hypotension, tachycardia, vasculitis

Central nervous system: Confusion, decreased sexual activity

Dermatologic: Alopecia, erythema multiforme, exfoliative dermatitis, skin rash, Stevens-Johnson syndrome, toxic epidermal necrolysis

Gastrointestinal: Nausea, pancreatitis, vomiting

Genitourinary: Breast swelling

Hematologic & oncologic: Agranulocytosis, aplastic anemia, hemolytic anemia (immune-based), neutropenia, pancytopenia, thrombocytopenia

Hepatic: Hepatic fibrosis (case report), increased serum ALT, increased serum AST

Hypersensitivity: Anaphylaxis

Neuromuscular & skeletal: Arthralgia, myalgia, polymyositis

Renal: Increased serum creatinine, interstitial nephritis

Respiratory: Pneumonia (causal relationship not established)

Miscellaneous: Fever

Warnings/Precautions

Concerns related to adverse effects:

• Confusion: Rare cases of reversible confusion have been associated with cimetidine; usually elderly or severely ill patients, or in patients with renal or hepatic impairment.

• Vitamin B12 deficiency: Prolonged treatment (≥2 years) may lead to vitamin B12 malabsorption and subsequent vitamin B12 deficiency. The magnitude of the deficiency is dose-related and the association is stronger in females and those younger in age (<30 years); prevalence is decreased after discontinuation of therapy (Lam 2013).

Disease-related concerns:

• Gastric malignancy: Relief of symptoms does not preclude the presence of a gastric malignancy.

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

• Renal impairment: Use with caution in patients with renal impairment; dosage adjustment recommended.

Concurrent drug therapy issues:

• Drug-drug interactions: Potentially significant interactions may exist, requiring dose or frequency adjustment, additional monitoring, and/or selection of alternative therapy. Consult drug interactions database for more detailed information.

Special populations:

• Elderly: Use caution in this age group due to risk of confusion and other CNS effects.

• Immunocompromised patients: May have increased risk of hyperinfection of strongyloidiasis.

• Pediatric: Use of gastric acid inhibitors, including proton pump inhibitors and H2 blockers, has been associated with an increased risk for development of acute gastroenteritis and community-acquired pneumonia in pediatric patients (Canani 2006).

Other warnings/precautions:

• OTC labeling: When used for self-medication (OTC), notify health care provider before use if any of the following are present: Frequent chest pain; frequent wheezing particularly with heartburn; nausea/vomiting; unexplained weight loss; stomach pain; heartburn >3 months; heartburn with light-headedness, sweating, or dizziness; chest pain or shoulder pain with shortness of breath; sweating or pain that spreads to arms, neck, or shoulders; light-headedness. Stop use and notify health care provider if heartburn continues or worsens, stomach pain continues, or if use is required >14 days.

Monitoring Parameters

CBC, gastric pH; monitor renal function to correct dose; occult blood with GI bleeding; signs of confusion.

Pregnancy Risk Factor

B

Pregnancy Considerations

Adverse events have not been observed in animal reproduction studies. Cimetidine crosses the placenta (Howe 1981). Histamine H2 antagonists have been evaluated for the treatment of gastroesophageal reflux disease (GERD), as well as gastric and duodenal ulcers during pregnancy (Cappell 2003; Richter 2003). Histamine H2 antagonists may be used for aspiration prophylaxis prior to cesarean delivery (ASA 2007).

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?)

• Have patient report immediately to prescriber signs of hepatic impairment, signs of pancreatitis, urinary retention, oliguria, tachycardia, bradycardia, arrhythmia, illogical thinking, mood changes, hallucinations, male macromastia, or sexual dysfunction (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 healthcare 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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