No abstract

No abstract

ABSTRACT:HIV protease inhibitors are essential components of most recommended treatment regimens for HIV infection. They are always coadministered with ritonavir as a pharmacokinetic booster. Their bioavailability may be impaired because they are substrates of CYP3A4 and several transporters, including P-glycoprotein. The aim of this study was to explore the impact of ritonavir on the intestinal absorption of HIV protease inhibitors in two models: the Caco-2 system and the in situ intestinal perfusion model with mesenteric blood sampling in mice. Using the Caco-2 system, the effect of ritonavir on the permeability of the other HIV protease inhibitors was significant for saquinavir (2-fold increase) and indinavir (3-fold increase), negligible for darunavir and amprenavir, and nonexistent for nelfinavir, lopinavir, tipranavir, and atazanavir.However, performing the in situ intestinal perfusion technique in mice for three selected HIV protease inhibitors showed a significant increase in the intestinal permeability for all: indinavir (3.2-fold), lopinavir (2.3-fold), and darunavir (3-fold). The effect of aminobenzotriazole (a nonspecific cytochrome P450 inhibitor) on lopinavir permeability was comparable with using ritonavir, whereas there was no effect for indinavir and darunavir. We conclude that ritonavir can boost drug absorption by inhibiting P-glycoprotein and/or metabolism, in a compound-specific manner. The results of this study illustrate that a combination of absorption models needs to be considered to elucidate drug-drug interactions at the level of the intestinal mucosa.

Food can have a significant impact on the pharmacokinetics of orally administered drugs, as it may affect drug solubility as well as permeability. Since fed state conditions cannot easily be implemented in the presently available permeability tools, including the frequently used Caco-2 system, exploring food effects during drug development can be quite challenging. In this study, we investigated the effect of fasted and fed state conditions on the intestinal absorption of the HIV protease inhibitor indinavir using simulated and human intestinal fluids in the in situ intestinal perfusion technique in mice. Although the solubility of indinavir was 6-fold higher in fed state human intestinal fluids (FeHIF) as compared to fasted state HIF (FaHIF), the intestinal permeation of indinavir was 22-fold lower in FeHIF as compared to FaHIF. Dialysis experiments showed that only a small fraction of indinavir is accessible for absorption in FeHIF due to micellar entrapment, possibly explaining its low intestinal permeation. The presence of ritonavir, a known P-gp inhibitor, increased the intestinal permeation of indinavir by 2-fold in FaHIF, while there was no increase when using FeHIF. These data confirm that drug-food interactions form a complex interplay between solubility and permeability effects. The use of HIF in in situ intestinal perfusions holds great promise for biorelevant absorption evaluation as it allows to directly explore this complex solubility/permeability interplay on drug absorption.

ABSTRACT: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 M) 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 M (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. IntroductionThe combination of multiple antiretroviral drugs with different modes of action (highly active antiretroviral therapy) has contributed to a spectacular progress in the fight against HIV (Hammer et al., 2008). The standard regimen for newly diagnosed patients usually includes two nucleoside reverse transcriptase inhibitors combined with either a protease inhibitor [boosted with ritonavir (RTV)] or a non-nucleoside reverse transcriptase inhibitor. Darunavir [(DRV) Prezista; Tibotec Pharmaceuticals, Cork, Ireland] is a second-generation protease inhibitor (PI) designed to have antiviral efficacy against HIV-1 with multiple resistance mutations to protease inhibitors (Busse and Penzak, 2007;Tremblay, 2008). RTV is always coadministered in a subtherapeutic dose as a pharmacokinetic booster of DRV.In vitro and in vivo studies have demonstrated that all HIV PI are high-affinity substrates for P-glycoprotein [(P-gp) multidrug resistance 1 (MDR1)], which can significantly influence the disposition of antiretroviral drugs (Kis et al., 2009). P-gp is widely distributed with a high level of expression in the small intestine, liver, kidney, and brain (Ho and Kim, 2005). Presently, however, there is still uncertainty about the role of intestinal P-gp in vivo. It is not sure whether P-gp plays a pivotal role as a biochemical barrier for compounds at concentrations relevant for the intraluminal environment, because of a possible saturation of the efflux system. In addition, it has b...