Phenytoin, plasma or serum

Phenytoin is one of the most widely prescribed drugs for the treatment of seizure disorders. It is considered one of the drugs of choice for generalized major motor and focal seizures. Strong correlation has been observed between serum levels and both therapeutic and toxic effects. The primary pathway for phenytoin elimination (90%) involves a metabolic conversion to 5(4-hydroxyphenyl)-5-phenylhydantoin (HPPH) which is a saturable process that could lead to toxic serum levels with a small increase in dosage. Phenytoin toxicity primarily affects the centrol nervous sytem. Chromic treatment may lead to hyperplasia of the gums, anemia and osteomalacia. Because both metabolism and clearance are highly variable among individuals, a close monitoring of serum levels is appropriate for virtually every patient undergoing phenytoin therapy.