Pharmacokinetics of carbamazepine. Part I: A new bioequivalency parameter based on a relative bioavailability trial.

The relative bioavailability of three carbamazepine generics available in Turkey, were investigated in 5 healthy male volunteers. When issuing a license to any drug, FDA stipulates at most a difference of 20% from the reference drug only in peak concentration and AUC (area under the curve). This condition may cause some problems, as two generics of the same drug can yield the same total amount (AUC) and can be accepted as bioequivalent despite different curves of the two drugs. In this study, to compare drugs from the point of view of bioequivalency, we suggest a new calculation method that takes into account ka (absorption rate constant), ke (elimination rate constant), tmax (time to peak), MRT (mean residence time) and AUC. Should this formula be used in comparison of bioequivalency, all the parameters related to the kinetics of drugs will have been taken into account. The suggested parameter is: [formula: see text] However, amongst three carbamazepine generics-Tegretol, Temporol and Karazepin-the most desirable curve is that of Tegretol, while bioavailability values are respectively F = 0.86, 0.93, 0.85 and AUC = 145, 161, 127. The A parameter values are respectively 49.3, 47.2, 42.9.