Solubility profiling of HIV protease inhibitors in human intestinal fluids

The present study pursued to profile the intestinal solubility of nine HIV protease inhibitors (PIs) in fasted- and fed-state human intestinal fluids (FaHIF, FeHIF) aspirated from four volunteers. In addition, the ability of fasted- and fed-state simulated intestinal fluids (FaSSIF, FeSSIF) to predict the intestinal solubility was evaluated. All PIs were poorly soluble in FaHIF (from 7 μM for ritonavir to 327 μM for darunavir) and FeHIF (from 15 μM for atazanavir to 409μM for darunavir). For four of nine PIs, food intake significantly enhanced the solubilizing capacity of intestinal fluids (up to 18.4-fold increase for ritonavir). The intersubject variability (average coefficient of variance CVfed = 60.6%, CVfasted = 40.4%) was higher as compared with the intrasubject variability (CVfed = 41.3%, CVfasted = 20.5%). PI solubilities correlated reasonably well between FaSSIF and FaHIF (R = 0.817), but not between FeSSIF and FeHIF (R = 0.617). To conclude, postprandial conditions increased the inter- and intrasubject variability of the PIs. The inability of FeSSIF to accurately predict the FeHIF solubility emphasizes the need for a multivariate approach to determine solubility profiles, taking into account solid-state characteristics, pH, mixed bile acid/phospholipid micelles, and digestive products.