Purpose: The purpose of this study was to determine if the intestinal transport of pregabalin (isobutyl gamma-aminobutyric acid, isobutyl GABA), a new anticonvulsant drug, was mediated by amino acid carriers with affinity for large neutral amino acids (LNAA).
Methods: Pregabalin transport was studied in rat intestine and Caco-2 monolayers. An in vitro Ussing/diffusion chamber model and an in situ single-pass perfusion model were used to study rat intestinal transport. An in vitro diffusion chamber model was used to evaluate Caco-2 transport.
Results: In rat ileum, pregabalin transport was saturable and inhibited by substrates of intestinal LNAA carriers including neurontin (gabapentin), phenylalanine, and proline. Weak substrates of intestinal LNAA carriers (beta-alanine, gamma-aminobutyric acid, and methyl aminoisobutyric acid) did not significantly change pregabalin transport. In Caco-2 monolayers that showed a high capacity for phenylalanine transport, pregabalin transport was concentration- and direction-independent and equivalent in magnitude to the paracellular marker, mannitol. The in vitro and in situ rat ileal permeabilities of the LNAA carrier-mediated compounds neurontin, pregabalin, and phenylalanine correlated well with the corresponding in vivo human oral absorption.
Conclusions: The transport of pregabalin was mediated by LNAA carriers in rat ileum but not in Caco-2 monolayers. Caco-2 was not an appropriate model for evaluating the in vivo human oral absorption of pregabalin and neurontin.