Clinical features and management of poisoning due to phenytoin.

The widespread use of phenytoin results in frequent accidental and intentional toxicity. Metabolism is enzymatic and can be described by Michaelis-Menten kinetics. This results in an increased half-life in overdose situations and a protracted clinical course which may last a week or more. The primary toxicity is on the central nervous system. The most common initial finding in mild toxicity is nystagmus. As concentrations increase ataxia, decreased coordination, hyper-reflexia, slurred speech and diplopia may develop. Progressive increases result in confusion, lethargy and coma. Various methods tried to increase elimination including dialysis, haemoperfusion, diuresis and plasmaphoresis have been ineffective and are not without risk. Meticulous supportive care including ventilation if necessary should provide a good clinical outcome. Multiple-dose activated charcoal may be helpful in shortening the duration of symptoms.