Phenytoin is an anticonvulsant drug which can be useful in the treatment of epilepsy. Phenytoin levels must be maintained within a narrow therapeutic range. Side effects and adverse reactions during initial dosage adjustment include: swelling of the gums and/or lymph nodes, hirsutism, insomnia, nausea, confusion, difficulty swallowing, fatigue, and rash. The phenytoin test is ordered to measure and monitor the amount of phenytoin in the blood and to determine whether drug concentrations are in the therapeutic range. VERY LOW levels may cause seizures. VERY HIGH levels are associated with toxicity and may cause loss of balance and falling, nystagmus (eye movement from side to side), confusion, slurred speech, tremors, or low blood pressure.
Phenytoin (epanutin): Collect sample at least 2 Hrs after completion of IV dose or 4 Hrs after IM dose. Sample stable for 7 days at 2-8°C.