Antiopyrine half-life as a measure of hepatic enzyme induction: clinical applications in a chronic epileptic population.

Quantitation of hepatic microsomal enzyme induction in epilepsy has a theoretical role in identifying patients at risk of metabolic bone disease, in assessing drug compliance and in predicting anticonvulsant dose/serum level relationships. The clinical usefulness of antipyrine half-life as a measure of enzyme induction in chronic epilepsy has been explored in this study. Mean antipyrine half-life in a control group (mean 10.7 hours SD 2.0) was significantly longer than in an epileptic group (mean 5.6 hours SD 2.3). Antipyrine t1/2 did not distinguish epileptics with osteomalacia from other epileptic patients and half-lives were similar in patients treated with phenytoin and a barbiturate to those in patients on phenytoin alone. No significant correlation was found between antipyrine half-life and phenytoin dose or between half-life and phenytoin level. In 5 patients with low serum levels of anticonvulsant, antipyrine kinetics suggested poor compliance in 3 and rapid hepatic phenytoin degradation in 2. This study suggests that measurement of antipyrine half-life may be useful in assessing drug compliance, but is not useful in predicting the onset of osteomalacia or dose/serum level relationships.