The efficacy of phenytoin in relation to serum levels in severe pre‐eclampsia and eclampsia

Abstract

Objectives To investigate the efficacy of phenytoin in relation to total and free serum levels in patients with severe pre-eclampsia and eclampsia. Design Prospective descriptive study. Setting Labour Ward, King Edward VIII Hospital, Durban, South Africa. Tertiary referral centre serving an underprivileged community. Subjects Eleven patients admitted with a hypertensive crisis. Four patients had eclampsia and 7 had impending eclampsia. Main outcome measures Free and total phenytoin levels; efficacy of phenytoin as an anticonvulsant and side-effects of therapy. Results Although total phenytoin levels were within the therapeutic range, free phenytoin levels were abnormally high in all patients. Three patients (2 with eclampsia and 1 with imminent eclampsia) each had a seizure after phenytoin treatment had been initiated. Conclusion Neither total nor free phenytoin levels were good predictors of seizure control. It is postulated that the poor performance of phenytoin as an anticonvulsant in severe eclampsia may relate to inadequate distribution of the drug to the brain as a result of cerebral oedema and poor cerebral perfusion rather than paradoxical seizure activity associated with high free phenytoin levels.