EFFECT OF A HIGH-PROTEIN MEAL ON GABAPENTIN PHARMACOKINETICS

The anticonvulsant, gabapentin is transported across biological membra nes via the L-amino acid transport system (System-L). Absorption of ga bapentin is saturable, and in-vitro data have previously demonstrated that both L-leucine and L-phenylalanine may compete with the intestina l transport of gabapentin. The purpose of this study therefore was to determine whether a high-protein meal would interfere with gabapentin absorption. Ten healthy volunteers received in a randomized, cross-ove r design, a single 600-mg dose of gabapentin in the fasting state and after a high-protein meal consisting of 80 gm total protein (4.1 g phe nylalanine, 8.2 g leucine and 4.2 g isoleucine), 52 g carbohydrate, an d 9 g fat. Plasma gabapentin concentrations were measured by HPLC at b aseline, 0.25, 0.5, 0.75, 1, 1.5, 2, 2.5, 3, 3.5, 4, 5, 6, 8, 12, 24, 30 h. Calculated pharmacokinetic parameters included C-max, T-max, AUC and T-1/2. In addition, a pharmacodynamic assessment (using visual an alog scales) of gabapentin-related adverse effects was performed at 2 h post drug ingestion and was compared between study phases. Statistic al analysis included Student's t-test for paired data, with significan ce assigned at P < 0.05. C-max was significantly increased by 36% (3.8 7 +/- 1.15 vs 5.28 +/- .97 mu g/ml, P = 0.002), and T-max tended to be shorter (3.9 +/- 1.8 vs 2.8 +/- .35 h, P = 0.10), after the high-prot ein meal. Although AUC was increased by 11%, this did not achieve stat istical significance. Despite significantly higher plasma concentratio ns at 2 h, subjects reported significantly fewer adverse effects after the high-protein meal. Potential mechanisms to explain these unexpect ed findings may be that the large amino acid load delivered with the h igh-protein meal enhanced gabapentin absorption via trans-stimulation, the process by which acutely increased intestinal luminal amino acid concentrations result in an acute up regulation in System-L activity. Conversely, the decrease in perceived adverse CNS effects of gabapenti n following the high-protein meal may reflect CNS competition for Syst em-L transport.