Phenytoin levels in catamenial epilepsy.

We studied the fluctuations in phenytoin (PHT) levels during ovulatory and menstrual phases of the cycle, in eight patients with catamenial epilepsy and in eight age-matched controls. Pharmacokinetic studies of PHT were done in five patients with catamenial epilepsy. The difference in PHT levels during menstrual and ovulatory phase in catamenial group was 3.44 +/- 3.25 micrograms/ml as compared with 0.91 +/- 2.03 micrograms/ml in controls. The mean fall during menstrual phase was significant (p less than 0.05) in the catamenial group. There was also rapid though statistically nonsignificant clearance of PHT during menses as compared with the ovulatory period. It is presumed that the fall in plasma PHT levels during menses, though still within therapeutic range, may be responsible for catamenial exacerbation of epilepsy.