There are several generic formulations of lamotrigine in Serbia that are widely used in the treatment of patients with epilepsy. The reduction of medical costs with use of generic formulations has potential risk because of the nature of disease, and it is necessary to investigate bioequivalence of each of generic formulations. Aim: Comparison of the efficacy of the reference and generic formulation of lamotrigine and theinvestigation of lamotrigine serum concentrations variation. Date were

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... red with in vitro results of dissolution profiles of the reference and generic tablet formulation. Patients (or Materials) and Methods: Lamotrigine steady-state concentrations were determined by high-performance liquid chromatography. In clinical study 16 patients participated, of whom 9 received reference formulation and 7 patients received generic formulation. Dissolution characteristics were evaluated at 3 points at physiologic pH range (pH 1.2, pH 4.5, pH 6.8), and difference (f1) and similarity (f2) tests were applied to dissolution data. Results: The relationship between lamotrigine serum concentration (µg/mL) and lamotrigine dose (mg/kg/d) were linear in both formulations (r 2 = 0.78484 original and r 2 = 0.83417 generic). There are statistically significant lower lamotrigine serum concentrations in patient treated with original formulation (3.97 [4.1] µg/mL) than those in patients treated with generic formulations (5.78 [2.7] µg/ mL). No dose-dependent adverse effects appeared in the patients, though patients treated with generic drug were receiving higher doses due to assumption that they are less potent. Brand drug had a lower standard deviation (SD) and data scattering because, as the dissolution data showed, it is less influenced by pH changes. Further dissolution profiles of 2 formulations were only similar in pH 1.2 medium. Conclusion: Investigation showed equal efficacy of 2 lamotrigine formulations, and the variations in plasma concentrations are probably due to individual characteristics of patients and differences in liberation rate of drugs in 2 formulations. It can be claimed that even if there are differences in dissolution profiles of 2 drugs they can have equal therapeutic efficacy.