DOES PERCENT REDUCTION IN SEIZURE FREQUENCY CORRELATE WITH PLASMA-CONCENTRATION OF ANTICONVULSANT DRUGS - EXPERIENCE WITH 4 ANTICONVULSANT DRUGS

Objective: To investigate the relationship between the percentage redu ction in seizure frequency in patients with epilepsy and plasma concen trations after oral administration of 4 anticonvulsant drugs, Methods: Patients with a minimum of 25% reduction in their seizure frequency f rom their baseline value were declared responders. The percentage redu ction in seizure frequency was plotted against plasma concentrations w ith use of pharmacodynamic models (Linear, log-linear, E-max, and sigm oidal E-max models). Zn addition to pharmacodynamic models, a logistic regression model was also fitted to the concentration-response data, with a value of 1 for responders and 0 for nonresponders, Results: The concentration-effect relationship could not be adequately described e ither by the pharmacodynamic models or by the logistic regression anal ysis. Conclusions: Based on the results obtained from both pharmacodyn amic models and logistic regression analysis the percentage reduction in seizure frequency may not be a true surrogate marker for anticonvul sant drugs to establish a pharmacodynamic relationship with plasma con centrations.