Effect of dosage frequency of carbamazepine on drug serum levels in epileptic patients.

The effect of dosage frequency of carbamazepine (CBZ) (brand name Tegretol) on pseudo-steady state drug serum levels were studied in 14 male (16-18 years) epileptics. They had already been receiving CBZ (mean dose 13.7 mg/kg) for an average period of 2.3 years in combination with other antiepileptic drugs. During this investigation, total daily CBZ dose was kept unaltered, but they received medication in thrice, twice and once daily dosage regimes. Each treatment period lasted for 4 weeks. The profiles of 24 h serum drug levels as assessed at the end of each treatment period, were observed to be within the therapeutic range during these 3 regimes. However, as expected, there were higher fluctuations of serum CBZ concentrations during once daily medication than during divided dosage regimes. Other concomitant antiepileptic drugs were continued in 2-3 divided daily doses during these 3 treatment periods, and the serum drug levels were measured at 8 h prior to the morning dosing. The concentrations of other drugs remained unchanged apart from a slight decrease in the serum sodium valproate levels during once daily medication. No clinical or electroencephalographic adverse effects were observed and there was no significant change in the fit frequency. In view of this observation, CBZ (Tegretol tablet) is probably effective as a single daily dose, but further long-term controlled clinical trial is necessary.