Another mechanism of interaction is possibly through the MDR1 (multidrug resistance protein 1) that is localized in the brush border of the enterocytes. P-glycoprotein (Pgp) transports lipophilic molecules out of the enterocyte back into the intestinal lumen. Drugs that possess lipophilic properties are either metabolised by CYP3A4 or removed into the intestine by the Pgp transporter. Both the Pgp and CYP3A4 may act synergistically as a barrier to many orally administered drugs. Therefore, their inhibition (both or alone) can markedly increase the bioavailability of a drug.