Less than 5% of phenytoin is cleared by renal clearance.39 Nevertheless, renal impairment has significant effects on phenytoin pharmacokinetics. Because of decreased protein binding in renal failure, the following occur:61
These changes can lead to overdosing of phenytoin if the dosing rate is based upon the total phenytoin plasma concentration. Monitoring of the free phenytoin plasma concentration is preferred in patients with renal insufficiency.
Phenytoin is poorly soluble in water, is 90% protein bound, and has a modest volume of distribution. As predicted, little phenytoin (2% to 4%) is lost in hemodialysis,62 peritoneal dialysis,63 or continuous ambulatory peritoneal dialysis.64 In a patient undergoing plasmapheresis, 10% of total phenytoin was removed with each treatment.65
Reviewed and revised February 2004 by Steven C. Schachter, MD, epilepsy.com Editorial Board.
© 2014 Epilepsy.com. All rights reserved.