Monitoring drug noncompliance in epileptic patients: assessing phenobarbital plasma levels.

In an attempt to detect drug noncompliance in epileptic patients, we assessed phenobarbital plasma concentrations and examined the determinants of noncompliance in 252 outpatients, with 22 inpatients as controls. The plasma level of phenobarbital was measured at least twice, at mean intervals of 4.8 months. The percent difference (PD) between the minimum and maximum levels was calculated in each case. A PD of more than 35% was associated with noncompliance. The frequency of noncompliance was 19% in the outpatient group. The medication period, seizure-free period, and, secondarily, number of drugs and drug forms were found to be correlated with noncompliance. Noncompliance was not influenced by the age of the patient, sex, psychomotor development, or seizure type or frequency. The mean period until complete control of seizures was significantly shorter in compliant than in noncompliant patients.