Phenytoin

Phenytoin chewable tablets are indicated for the treatment of generalized tonic-clonic (grand mal) and complex partial (psychomotor, temporal lobe) seizures and prevention and treatment of seizures occurring during or following neurosurgery. Phenytoin chewable tablets are indicated for the treatment of generalized tonic-clonic (grand mal) and complex partial (psychomotor, temporal lobe) seizures and prevention and treatment of seizures occurring during or following neurosurgery. ( 1 )

• NOT FOR ONCE-A-DAY DOSING • Adult starting dose in patients who have received no previous treatment is two phenytoin chewable tablets three times a day, with dose adjustments as necessary
• For most
• Adults, the satisfactory maintenance dose will be six to eight phenytoin chewable tablets daily; an increase to twelve phenytoin chewable tablets daily may be made, if necessary. • Pediatric starting dose is 5 mg/kg/day in two to three equally divided doses, with dosage adjustments as necessary, up to a maximum of 300 mg daily
• Maintenance dosage is 4 mg/kg/day to 8 mg/kg/day. • Serum blood level determinations may be necessary for optimal dosage adjustments—the clinically effective serum total concentration is 10 mcg/mL to 20 mcg/mL (unbound phenytoin concentration is 1 mcg/mL to 2 mcg/mL)
• Important Administration Instructions NOT FOR ONCE-A-DAY DOSING
• Phenytoin chewable tablets can be either chewed thoroughly before being swallowed or swallowed whole
• Adult Dosage The recommended starting dosage for adult patients who have received no previous treatment is two 50 mg phenytoin chewable tablets by mouth three times daily
• Adjust the dosage to suit individual requirements up to a maximum of twelve phenytoin chewable tablets daily
• For most
• Adults, the satisfactory maintenance dosage will be six to eight phenytoin chewable tablets daily. …

Phenytoin chewable tablets are available as 50 mg phenytoin yellow, round, scored chewable tablets. Phenytoin chewable tablets are available as 50 mg scored chewable tablets. ( 3 )

• Initially, 5 mg/kg/day in two or three equally divided doses, with subsequent dosage individualized to a maximum of 300 mg daily
• A recommended daily maintenance dosage is usually 4 mg/kg to 8 mg/kg
• Children over 6 years and adolescents may require the minimum adult dosage (300 mg/day) [see Dosage and Administration ]

Phenytoin clearance tends to decrease with increasing age [see Clinical Pharmacology (12.3) ] . Lower or less frequent dosing may be required [see Dosage and Administration (2.7) ] .

• Advise patients to read the FDA-approved patient labeling (Medication Guide)
• Administration Information Advise patients taking phenytoin 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 orally as prescribed, e.g., surgery, etc
• Withdrawal of Antiepileptic Drugs Advise patients not to discontinue use of phenytoin without consulting with their healthcare provider
• Phenytoin should normally be gradually withdrawn to reduce the potential for increased seizure frequency and status epilepticus [see Warnings and Precautions ] . …

• Phenytoin chewable tablets are contraindicated in patients with: • A history of hypersensitivity to phenytoin, its inactive ingredients, or other hydantoins [see Warnings and Precautions ]
• Reactions have included angioedema. • A history of prior acute hepatotoxicity attributable to phenytoin [see Warnings and Precautions ] . …

Phenytoin is extensively bound to plasma proteins and is prone to competitive displacement. Phenytoin is primarily metabolized by the hepatic cytochrome P450 enzyme CYP2C9 and to a lesser extent by CYP2C19, and is particularly susceptible to inhibitory drug interactions because it is subject to saturable metabolism. Inhibition of metabolism may produce significant increases in circulating phenytoin concentrations and enhance the risk of drug toxicity. Monitoring of phenytoin serum levels is recommended when a drug interaction is suspected. Phenytoin is a potent inducer of hepatic drug-metabolizing enzymes. …

• Withdrawal Precipitated Seizure: May precipitate status epilepticus. Dose reductions or discontinuation should be done gradually. ( 5.1 ) • Suicidal Behavior and Ideation: Monitor patients for the emergence or worsening of depression, suicidal thoughts or behavior, and/or any unusual changes in mood or behavior. ( 5.2 ) • Serious Dermatologic Reactions: Discontinue phenytoin chewable tablets at the first sign of a rash, unless the rash is clearly not drug-related. If signs or symptoms suggest SJS/TEN, use of this drug should not be resumed and alternative therapy should be considered. …

The following serious adverse reactions are described elsewhere in the labeling: • Withdrawal Precipitated Seizure, Status Epilepticus [see Warnings and Precautions (5.1) ] • Suicidal Behavior and Ideation [see Warnings and Precautions (5.2) ] • Serious Dermatologic Reactions [see Warnings and Precautions (5.3) ] • Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS)/Multiorgan Hypersensitivity [see Warnings and Precautions (5.4) ] • Hypersensitivity [see Warnings and Precautions (5.5) ] • Cardiac Effects [see Warnings and Precautions (5.6) ] • Angioedema [see Warnings and Precautions (5.7) ] • Hepatic Injury [see Warnings and Precautions (5.8) ] • Hematopoietic Complications [see W …

8.1 Pregnancy Pregnancy Exposure Registry There is a pregnancy exposure registry that monitors pregnancy outcomes in women exposed to antiepileptic drugs (AEDs), such as phenytoin, during pregnancy. Physicians are advised to recommend that pregnant patients taking phenytoin enroll in the North American Antiepileptic Drug (NAAED) Pregnancy Registry. …

The lethal dose in pediatric patients is not known. The lethal dose in adults is estimated to be 2 grams to 5 grams. The initial symptoms are nystagmus, ataxia, and dysarthria. Other signs are tremor, hyperreflexia, lethargy, slurred speech, blurred vision, nausea, and vomiting. The patient may become comatose and hypotensive. Bradycardia and cardiac arrest have been reported [see Warnings and Precautions (5.6) ] . Death is caused by respiratory and circulatory depression. There are marked variations among individuals with respect to phenytoin serum levels where toxicity may occur. …

Store at 20° to 25°C (68° to 77°F) [see USP Controlled Room Temperature]. Protect from moisture.

Take it when you remember, unless it is nearly time for the next dose. Then skip the missed one. Never take two doses at once to make up for it. Check your leaflet, as some medicines are different.