Changes in carbamazepine plasma concentrations in psychiatric patients during treatment

Plasma concentrations of carbamazepine (CBZ) were studied in 24 psychiatric patients who were given 400 mg of CBZ every 12 h. The assays were performed on the 1st, 3rd, 8th, 15th, 22th and 29th day of the therapy. The highest minimum 12h plasma CBZ concentrations occurred on the 3rd day of therapy, then decreased up to the 15th day and remained stable thereafter. The CBZ half-time values also diminished up to the 15th day of therapy and then stabilized. This may suggest that the enzymatic autoinduction of CBZ is completed within the first 1-2 weeks of therapy. CBZ plasma levels were slightly but insignificantly higher in patients taking CBZ alone than in patients in which CBZ was added to other psychotropic drugs. A significant correlation was found between the minimum CBZ plasma concentration after the first dose and that at steady state. A dosing schedule for CBZ administration has been proposed with administration of 75% of the maintenance dose during the first week and the full CBZ maintenance dose from the beginning of the second week of CBZ therapy.