TY - JOUR T1 - In Situ Intestinal Perfusion in Knockout Mice Demonstrates Inhibition of Intestinal P-Glycoprotein by Ritonavir Causing Increased Darunavir Absorption JF - Drug Metabolism and Disposition JO - Drug Metab Dispos SP - 1407 LP - 1410 DO - 10.1124/dmd.110.032771 VL - 38 IS - 9 AU - Nico Holmstock AU - Raf Mols AU - Pieter Annaert AU - Patrick Augustijns Y1 - 2010/09/01 UR - http://dmd.aspetjournals.org/content/38/9/1407.abstract N2 - Darunavir is a second-generation protease inhibitor designed to have antiviral efficacy against HIV-1 with multiple resistance mutations to protease inhibitors. It is always coadministered with a subtherapeutic dose of ritonavir. It has been shown that darunavir and ritonavir are substrates of P-glycoprotein (P-gp). We explored the contribution of P-gp to the transport characteristics of darunavir (up to 100 μM) using Caco-2 monolayers and the recently developed in situ intestinal perfusion technique using wild-type and mdr1a/1b(−/−) mice. We observed that, in vitro, P-gp has a modulatory effect on the absorption of darunavir, even at a concentration of 100 μM (efflux ratio = 25). Simulated intestinal fluids partially inhibited P-gp functionality, which was further inhibited by adding the P-gp inhibitors verapamil, 6-[(2S,4R,6E)- 4-methyl-2-(methylamino)-3-oxo-6-octenoic acid]cyclosporine D (PSC833), N-(4-[2-(1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl) ethyl]-phenyl)-9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamide (GF120918), or ritonavir. Using the in situ intestinal perfusion technique, we demonstrated that coperfusion with ritonavir resulted in a similar apparent permeability coefficient to that observed using P-gp knockout mice, which was 2.7-fold higher than in control mice. We conclude that, in mice, even at a relevant intraluminal concentration of darunavir, P-gp has a modulatory effect on the absorption of darunavir. However, this P-gp-mediated darunavir transport is inhibited when it is combined with ritonavir. ER -