Relation between dosage of carbamazepine and concentration in hair and plasma samples from a compliant inpatient epileptic population

Compliance is a problem in all areas of therapeutic medicine. Methods for i ts assessment are classified as either indirect or direct. Indirect assessm ent is based on criteria such as pill counts, questionnaires, and self-repo rting; direct methods involve the analytic measurement of the drugs in biol ogic fluids such as plasma or urine. Drugs taken either therapeutically or recreationally become incorporated into hair. This prospective study invest igated the relation between the daily intake of the antiepileptic drug carb amazepine and both its trough plasma and hair concentrations in a highly su pervised inpatient population of patients with epilepsy during a period of 6 months. Results showed that although there was a significant variation be tween patients resulting from the substantial range in the daily intake of carbamazepine (800-2400 mg/day), the intrapatient variation in both trough plasma and hair concentrations during the 6-month period were not significa ntly different. The mean intrapatient percentage coefficient of variation i n total plasma and hair concentrations of carbamazepine was 11.5 +/- 4.7 an d 15.0 +/- 5.2, respectively, both of which were independent of the daily d osage. This relatively small intrapatient variation in hair concentration o ver time and its close relation to the plasma concentration suggests that h air analysis may be a complementary and useful technique in monitoring drug -taking behavior.