Teratogenic and pharmacokinetic studies of primidone during pregnancy and in the offspring of epileptic women.

Fourteen epileptic women treated with primidone, either alone or in combination with other antiepileptic drugs, were studied prospectively during their pregnancy. Plasma levels of primidone and its metabolites were monitored and correlated to findings in the offspring. Maternal serum concentrations of primidone and metabolites were generally low during pregnancy. The levels of its main metabolites--phenobarbital and PEMA--were found to drop within the first month of pregnancy in two cases. The plasma concentrations remained low until birth and rose sharply thereafter. The phenobarbital/primidone ratio (mean 0.84) and PEMA/primidone ratio (mean 0.56) in pregnant patients were found to be lower than in non-pregnant patients, except when primidone was given in combination with phenytoin in which case the expected phenobarbital/primidone (mean 2.5) and PEMA/primidone (mean 1.5) ratios were found. A ventricular septal defect was found in one of the offspring of the fourteen mothers and five children had microcephaly. There was a high incidence of poor somatic development with dystrophy (n=3) and short stature (n=2). Head circumferences (n=8), lengths (n=4) and/or weights (n=8) were below the 10th percentile in a number of children. Four children showed marked facial dysmorphy. Our preliminary data suggest that primidone intake during pregnancy may be important in the pathogenesis of minor anomalies and in the induction of poor somatic development.