While inhibition of CYP3A4 delays drug metabolism and consequently increases plasma levels of affected drugs, grapefruit juice may also affect drug transport. In regard to drug efflux, grapefruit juice did not significantly affect digoxin pharmacokinetics, and thus is unlikely to be an important inhibitor of P-gp function. However, one in vitro study has demonstrated impaired uptake of the antihistamine fexofenadine in epithelial cells transfected with OATP1A2. The possible role of grapefruit juice as an inhibitor of OATP was further extended in clinical studies. Indeed, this pathway of inhibition by grapefruit juice may play an important role in regard to drugs, such as fexofenadine, that are not metabolized by either hepatic or intestinal CYP3A4.