Boosting of HIV protease inhibitors by ritonavir in the intestine: the relative role of cytochrome P450 and P-glycoprotein inhibition based on Caco-2 monolayers versus in situ intestinal perfusion in mice.

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.