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Phenytoin Dosage

Applies to the following strength(s): 50 mg/mL ; 50 mg ; 100 mg ; 30 mg ; 25 mg/mL ; 200 mg ; 300 mg ; sodium

The information at Drugs.com is not a substitute for medical advice. Always consult your doctor or pharmacist.

Usual Adult Dose for:

Usual Pediatric Dose for:

Additional dosage information:

Usual Adult Dose for Seizures

EXTENDED RELEASE FORMULATION (100 mg per capsule):
-DIVIDED DAILY DOSAGE:
Initial dose (in patients not previously treated with this drug): 1 capsule orally 3 times a day; dosage then adjusted to suit individual requirements
Maintenance dose: For most adults the satisfactory maintenance dosage will be 1 capsule 3 to 4 times a day; for others an increase up to 2 capsules 3 times a day may be made, if necessary
-ONCE-A-DAY DOSAGE:
If seizure control is established with divided doses of 3 capsules orally daily, then 300 mg orally once a day may be considered
-LOADING DOSE:
Some clinicians use an oral loading dose in adults who require rapid steady-state serum levels and where IV administration is not desirable. This dosing regimen should be reserved for patients in a clinic or hospital setting where phenytoin serum levels can be closely monitored. Patients with a history of renal or liver disease should not receive the oral loading regimen: Initially, 1 gm is divided into 3 doses (400 mg, 300 mg, 300 mg) and administered at 2 hour intervals. Normal maintenance dosage is then instituted 24 hours after the loading dose, with frequent serum level determinations.

CHEWABLE TABLETS (50 mg per tablet):
Initial dose (in patients not previously treated with this drug): 2 tablets chewed 3 times a day; dosage then adjusted to suit individual requirements; for most adults, the satisfactory maintenance dosage will be 6 to 8 tablets daily; an increase to 12 tablets daily may be made, if necessary

SUSPENSION (125 mg per 5 mL):
Initial dose (in patients not previously treated with this drug): 5 mL orally 3 times daily; dosage then adjusted to suit individual requirements; an increase to 25 mL orally daily may be made, if necessary

Use: For the control of tonic-clonic (grand mal) and psychomotor (temporal lobe) seizures

Usual Adult Dose for Status Epilepticus

IV: Treatment can be initiated either with a loading dose or an infusion:
-LOADING DOSE: 10 to 15 mg/kg by slow IV infusion, not exceeding 50 mg/min; infusion must be completed within 1 to 4 hours
IV/ORAL:
Maximum rate: 50 mg/min
-NONEMERGENT LOADING AND MAINTENANCE DOSING: Because of the risks of cardiac and local toxicity associated with IV administration, oral dosing should be used whenever possible:
LOADING DOSE: 10 to 15 mg/kg IV (not to exceed 50 mg/min in adults)
MAINTENANCE DOSE: The loading dose should be followed by maintenance doses by oral or IV administration every 6 to 8 hours
-IM: Ordinarily, this drug should not be given IM because of the risk of necrosis, abscess formation, and erratic absorption. If IM administration is required, compensating dosage adjustments are necessary to maintain therapeutic plasma levels. An IM dose 50% greater than the oral dose is necessary to maintain these levels. When returned to oral administration, the dose should be reduced by 50% of the original oral dose for 1 week to prevent excessive plasma levels due to sustained release from IM tissue sites.

Comments:
-Electrocardiogram and blood pressure should be monitored continuously.
-The patient should be observed for signs of respiratory depression.
-Phenytoin plasma levels should be obtained in the management of status epilepticus and in the subsequent establishment of maintenance dosage.
-Other measures, including concomitant administration of an IV benzodiazepine such as diazepam, or an IV short-acting barbiturate, will usually be necessary for rapid control of seizures because of the required slow rate of administration of phenytoin.
-If IV administration does not terminate seizures, the use of other anticonvulsants, IV barbiturates, general anesthesia and other appropriate measures should be considered.
-IM administration should not be used in the treatment of status epilepticus because the attainment of peak plasma levels may require up to 24 hours.

Use: For the control of generalized tonic-clonic status epilepticus

Usual Adult Dose for Seizure Prophylaxis During or Following Neurosurgery

-ORAL:
Initial dose: 5 mg/kg/day orally in 2 or 3 equally divided doses, with subsequent dosage individualized to a maximum of 300 mg orally daily
-Maintenance dose: 4 to 8 mg/kg. Children over 6 years old and adolescents may require the minimum adult dose (300 mg/day)

-IV:
Loading dose: Do not exceed an infusion rate of 1 to 3 mg/kg/min (or 50 mg per minute, whichever is slower) in pediatric patients

Comments:
-Because of the increased risk of adverse cardiovascular reactions associated with rapid IV administration, the rate should not exceed 1 to 3 mg/kg/min or 50 mg per minute in children, whichever is slower.

Use: For the prevention and treatment of seizures occurring during or following neurosurgery

Usual Pediatric Dose for Seizures

-ORAL:
Initial dose: 5 mg/kg/day orally in 2 or 3 equally divided doses, with subsequent dosage individualized to a maximum of 300 mg orally daily
-Maintenance dose: 4 to 8 mg/kg. Children over 6 years old and adolescents may require the minimum adult dose (300 mg/day)

Use: For the control of tonic-clonic (grand mal) and psychomotor (temporal lobe) seizures

Usual Pediatric Dose for Status Epilepticus

-IV:
-EMERGENT LOADING DOSE: 15 to 20 mg/kg by slow IV infusion (to produce plasma concentrations of phenytoin within the generally accepted therapeutic range of 10 to 20 mcg/mL); infusion must be completed within 1 to 4 hours
Maximum rate: 1 to 3 mg/kg/min or 50 mg/min, whichever is slower
Maintenance rate: 100 mg orally or IV every 6 to 8 hours
-NONEMERGENT LOADING AND MAINTENANCE DOSING: Because of the risks of cardiac and local toxicity associated with IV administration, oral dosing should be used whenever possible:
LOADING DOSE: 1 to 3 mg/kg/min (or 50 mg/min, whichever is slower)
MAINTENANCE DOSE: The loading dose should be followed by maintenance doses by oral or IV administration every 6 to 8 hours
-IM: Ordinarily, this drug should not be given IM because of the risk of necrosis, abscess formation, and erratic absorption. If IM administration is required, compensating dosage adjustments are necessary to maintain therapeutic plasma levels. An IM dose 50% greater than the oral dose is necessary to maintain these levels. When returned to oral administration, the dose should be reduced by 50% of the original oral dose for 1 week to prevent excessive plasma levels due to sustained release from IM tissue sites.

Comments:
-Electrocardiogram and blood pressure should be monitored continuously.
-The patient should be observed for signs of respiratory depression.
-Phenytoin plasma levels should be obtained in the management of status epilepticus and in the subsequent establishment of maintenance dosage.
-Other measures, including concomitant administration of an IV benzodiazepine such as diazepam, or an IV short-acting barbiturate, will usually be necessary for rapid control of seizures because of the required slow rate of administration of phenytoin.
-If IV administration does not terminate seizures, the use of other anticonvulsants, IV barbiturates, general anesthesia and other appropriate measures should be considered.
-IM administration should not be used in the treatment of status epilepticus because the attainment of peak plasma levels may require up to 24 hours.

Use: For the control of generalized tonic-clonic status epilepticus

Usual Pediatric Dose for Seizure Prophylaxis During or Following Neurosurgery

-ORAL:
Initial dose: 5 mg/kg/day orally in 2 or 3 equally divided doses, with subsequent dosage individualized to a maximum of 300 mg orally daily
-Maintenance dose: 4 to 8 mg/kg. Children over 6 years old and adolescents may require the minimum adult dose (300 mg/day)

-IV:
Loading dose: Do not exceed an infusion rate of 1 to 3 mg/kg/min (or 50 mg per minute, whichever is slower) in pediatric patients

Comments:
-Because of the increased risk of adverse cardiovascular reactions associated with rapid IV administration, the rate should not exceed 1 to 3 mg/kg/min or 50 mg per minute in children, whichever is slower.

Use: For the prevention and treatment of seizures occurring during or following neurosurgery

Renal Dose Adjustments

Due to an increased fraction of unbound phenytoin in patients with renal disease, the interpretation of total phenytoin plasma concentrations should be made with caution. Unbound phenytoin concentrations may be more useful.

Liver Dose Adjustments

Due to an increased fraction of unbound phenytoin in patients with hepatic disease, the interpretation of total phenytoin plasma concentrations should be made with caution. Unbound phenytoin concentrations may be more useful.

Dose Adjustments

-Elderly patients: A lower loading dose and/or infusion rate, and lower or less frequent maintenance dosing may be required. Phenytoin metabolism is slightly decreased in elderly patients.
-Serum concentrations should be monitored in changing from the extended release to the regular release formulation of this drug, and from the sodium salt to the free acid form. Because there is approximately an 8% increase in drug content with the free acid form over that of the sodium salt, dosage adjustments and serum level monitoring may be necessary when switching from a product formulated with the free acid to a product formulated with the sodium salt and vice versa.
-Dosage should be individualized to provide maximum benefit. In some cases, serum blood level determinations may be necessary for optimal dosage adjustments. The clinically effective serum level is usually 10 to 20 mcg/mL.
-With recommended dosage, a period of 7 to 10 days may be required to achieve steady-state blood levels and changes in dosage (increase or decrease) should not be carried out at intervals shorter than 7 to 10 days.

Precautions

US BOXED WARNINGS:
CARDIOVASCULAR RISK ASSOCIATED WITH RAPID INFUSION RATES:
-The rate of IV administration should not exceed 50 mg per minute in adults and 1 to 3 mg/kg/min (or 50 mg/min, whichever is slower) in pediatric patients because of the risk of severe hypotension and cardiac arrhythmias.
-Careful cardiac monitoring is needed during and after IV administration of this drug.
-Although the risk of cardiovascular toxicity increases with infusion rates above the recommended infusion rate, these events have also been reported at or below the recommended infusion rate. Reduction in rate of administration or discontinuation of dosing may be needed

Consult WARNINGS section for additional precautions.

Dialysis

Data not available

Other Comments

Administration advice:
-The IV administration rate of this drug should not exceed 50 mg per minute in adults and 1 to 3 mg/kg/min in pediatric patients because of the risk of severe hypotension and cardiac arrhythmias.
-Careful cardiac monitoring is needed during and after administering this drug IV. Although the risk of cardiovascular toxicity increases with infusion rates above the recommended infusion rate, these events have also been reported at or below the recommended infusion rate. Reduction in rate of administration or discontinuation of dosing may be needed.

Storage requirements:
-The manufacturer product information should be consulted.

Reconstitution/preparation techniques:
-The manufacturer product information should be consulted.

General:
-The IV formulation of this drug can be substituted, short-term, for the oral formulation, but only when oral administration is not possible.
-This drug may be administered by IV or IM injection; however, the IM route should not be used for the emergency control of seizures such as status epilepticus.
-When a change in the dosage form or brand is prescribed, careful monitoring of phenytoin serum levels should be carried out.
-Serum drug levels should be monitored when changing from extended release to prompt release and from the sodium salt to the free acid suspension and chewable tablets forms.
-Acute alcoholic intake may increase phenytoin serum levels while chronic alcoholic use may decrease serum levels.
-The concurrent administration of enteral feeding preparations and/or related nutritional supplements can reduce the oral absorption of this drug by up to 80%. When enteral feedings are stopped, phenytoin levels may rise significantly. In patients who can receive intermittent feedings, this drug should be administered at least 2 hours after a feeding and the next feeding should be delayed until at least 2 hours after the phenytoin dose. The IV formulation is recommended for patients who must receive continuous enteral feedings.

Patient advice:
-Inform patients of the availability of a Medication Guide, and instruct them to read the Medication Guide prior to taking this drug.
-Patients taking this drug should be advised of the importance of adhering strictly to the prescribed dosage regimen, and of informing the physician of any clinical condition in which it is not possible to take the drug as prescribed (e.g., surgery, etc.).
-Patients should be made aware of the early toxic signs and symptoms of potential hematologic, dermatologic, hypersensitivity, or hepatic reactions. These symptoms may include, but are not limited to, fever, sore throat, rash, ulcers in the mouth, easy bruising, lymphadenopathy and petechial or purpuric hemorrhage, and in the case of liver reactions, anorexia, nausea/vomiting, or jaundice. The patient should be advised that, because these signs and symptoms may signal a serious reaction, they should report any occurrence immediately to a physician even if mild or when occurring after extended use.
-Patients should be cautioned about the use of other drugs or alcoholic beverages without first seeking physician advice.
-The importance of good dental hygiene should be stressed in order to minimize the development of gingival hyperplasia and its complications.
-Patients, their caregivers, and families should be counseled that antiepileptic drugs (AEDs) may increase the risk of suicidal thoughts and behavior and should be advised of the need to be alert for the emergence or worsening of symptoms of depression, any unusual changes in mood or behavior, or the emergence of suicidal thoughts or behavior.

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