Phenytoin

DEA Class;  Rx

Common Brand Names; Dilantin, Dilantin 125, Phenytek

Hypersensitivity

Sinus bradycardia

Sinoatrial block

Second and third degree A-V block

Adams-Stokes syndrome

Concurrent use with delavirdine

History of prior acute hepatotoxicity attributable to phenytoin

• Drowsiness
• Fatigue
• Ataxia
• Irritability
• Headache
• Restlessness
• Slurred speech
• Nervousness
• Nystagmus
• Dizziness
• Vertigo
• Dysarthria
• Paresthesia
• Rash
• Pruritus
• Gingival hyperplasia (pediatric patients)
• Ataxia
• Paradoxical seizure
• Drug withdrawal seizure
• Diplopia
• Psychosis (high dose)
• Toxic amblyopia
• Encephalopathy
• AV conduction disorder
• Ventricular fibrillation
• Nausea
• Vomiting
• Constipation
• Diarrhea
• Megaloblastic (folate-deficiency) anemia
• Hypocalcemia
• Hepatotoxicity
• Hypertrichosis
• Lymphadenopathy, including benign lymph node hyperplasia, pseudolymphoma, lymphoma, and Hodgkin’s disease
• Purple glove syndrome
• Rash
• Allergic reactions in the form of rash or, rarely, more serious forms (drug reaction with eosinophilia and systemic symptoms, or DRESS) or anaphylaxis
• Purpuric rash
• Toxic epidermal necrolysis
• Bullous, exfoliative, or purpuric dermatitis
• Coarsening of facial features
• Periarteritis nodosa
• Immunoglobulin abnormalities
• Altered taste sensation, including metallic taste
• Peyronie disease

Erratically absorbed when administered IM, so this route should be used as a last resort

ONLY extended-release capsules should be used for once-daily dosing regimens

Decreased bone mineral density reported with chronic use

Rapid intravenous administration increases the risk of adverse cardiovascular reactions, including severe hypotension and cardiac arrhythmias; in pediatric patients, administer the drug at a rate not exceeding 1 to 3 mg/kg/min or 50 mg per minute, whichever is slower; although risk of cardiovascular toxicity increases with infusion rates above recommended infusion rate, these events have also been reported at or below recommended infusion rate

May cause fetal harm when administered to a pregnant woman

Phenytoin induces hepatic metabolizing enzymes, which may enhance metabolism of vitamin D and decrease vitamin D levels, leading to vitamin D deficiency, hypocalcemia, and hypophosphatemia; consideration should be given to screening with bone-related laboratory and radiological tests as appropriate and initiating treatment plans according to established guidelines

Use caution in cardiovascular disease, hypoalbuminemia, hepatic impairment, hypothyroidism, or seizures; because fraction of unbound phenytoin is increased in patients with renal or hepatic disease, or in those with hypoalbuminemia, the monitoring of phenytoin serum levels should be based on the unbound fraction in those patients

Associated with exacerbation of porphyria; exercise caution when used in patients with this disease

Extensively bound to serum plasma proteins and is prone to competitive displacement

Acute alcoholic intake may increase phenytoin serum levels, while chronic alcoholic use may decrease serum levels

Pregnancy: Pregnancy exposure registry that monitors pregnancy outcomes in women exposed to antiepileptic drugs (AEDs)

Lactation: Phenytoin is secreted in human milk; developmental and health benefits of breastfeeding should be considered along with mother’s clinical need for therapy and any potential adverse effects on breastfed infant from phenytoin or from underlying maternal condition