Epilepsy, myasthenia gravis, and effect of plasmapheresis on antiepileptic drug concentrations

C. W. Lai, I. E. Leppik, D. C. Jenkins and P. Sood
Department of Neurology, University of Kansas Medical Center, Kansas City 66103.

A 28-year-old woman developed complex partial seizures at the age of 17 years and was treated with phenytoin sodium. Five years later she developed myasthenia gravis, and phenytoin was replaced by valproic acid and phenobarbital. She required plasmapheresis (PP). During one course of PP, total and unbound concentrations of valproic acid and phenobarbital were measured in serum sampled before, during, and after PP and in plasma removed by PP. It was determined that the magnitude of loss of valproic acid or phenobarbital by PP was small, and the changes of unbound/total ratio did not reach clinical importance.