Pharmacokinetic Interactions between HIV-1 Protease Inhibitors in Rats: Study on Combinations of Two Kinds of HIV-1 Protease Inhibitors

Abstract

The drug interactions between four human immune deficiency virus (HIV-1) protease inhibitors have been characterized by in-vitro metabolic studies using rat liver microsomal fractions and in-vivo oral administration. In this study, a new HPLC analytical method developed by us was used for the simultaneous determination of saquinavir and nelfinavir in rat plasma and microsomes. The metabolic clearance rates (Vmax/Km) of saquinavir, nelfinavir, and indinavir were 170.9 +/- 10.9, 126.1 +/- 4-4, and 73.0 +/- 2.0 microL min(-1) (mg protein)(-1), respectively. Ritonavir was the strongest inhibitor with inhibition constants (Ki) of 1.64 microM for saquinavir, 0.95 microM for indinavir, and 1.01 microM for nelfinavir. Nelfinavir was the second strongest inhibitor with Ki's of 2.35 microM for saquinavir and 2.14 microM for indinavir. Indinavir was the third strongest inhibitor with Ki's of 2.76 microM for nelfinavir and 3.55 microM for saquinavir. Saquinavir was the weakest inhibitor for the other three HIV- 1 protease inhibitors. After oral co-administration in combination with another HIV-1 protease inhibitor, the AUCs of saquinavir, indinavir, and nelfinavir were significantly increased compared with mono-treatment. The AUCs of saquinavir were increased about 10.1-, 3.1- and 45.9-fold in the presence of indinavir, nelfinavir and ritonavir, respectively. The AUCs of indinavir were increased about 6.8-, 5.9- and 9.4-fold in the presence of nelfinavir, saquinavir and ritonavir, respectively. The AUCs of nelfinavir were increased about 2.2-, 6.6- and 8.5-fold in the presence of indinavir, saquinavir and ritonavir, respectively. The in-vivo effects observed after co-administration of two kinds of HIV-1 protease inhibitor were not always expected from in-vitro data, suggesting the presence of other interaction processes besides metabolism in the liver. These results provide useful information for the treatment of AIDS patients receiving combination therapy with two HIV-1 protease inhibitors.

Comparative Use of Isolated Hepatocytes and Hepatic Microsomes for Cytochrome P450 Inhibition Studies: Transporter-Enzyme Interplay

“…SQV and NFV exhibited competitive inhibition and no evidence of partial inhibition. The inhibitory potency for the inhibition of 1Ј-OH-midazolam observed in rat microsomes is comparable to results published by Shibata et al (2000).…”

“…For all four compounds, inhibition was clearly evident in the hepatocyte preparations, and this result is consistent with in vivo studies in both humans and rats (Edwards et al, 1988;Olkkola et al, 1993;Davis et al, 1994;Yamaji et al, 1999;Yamano et al, 1999;Shibata et al, 2000). The two protease inhibitors studied, SQV and NFV, were very potent inhibitors of midazolam hydroxylation with K i values Յ1 M. In the case of ENX and CLAR inhibition, K i values were much less potent in the region of 100 M. All compounds are known to be substrates for the solute carrier transporter proteins (Sasabe et al, 1997;Yamano et al, 1999;Su et al, 2004;Maeda et al, 2007;Seithel et al, 2007;Giacomini et al, 2010), thus there was an expectation that hepatocytes would show higher sensitivity to inhibition than microsomes.…”

“…In contrast, the hepatic clearance of the protease inhibitors is very high (Shibata et al, 2000;Parker and Houston, 2008). We have studied this in some detail in vitro and have dmd.aspetjournals.org demonstrated that in hepatocytes the metabolic clearance is transporter rate-limited (Parker and Houston, 2008).…”

Effect of Indinavir on the Intestinal Exsorption of Amprenavir, Saquinavir and Nelfinavir after Intravenous Administration in Rats.

“…31,32) In our previous studies on pharmacokinetic interactions among the HIV PIs currently used in clinical therapy, we observed that IDV inhibited the metabolism of APV, NFV and SQV with K i values of 0.67, 2.76 and 3.55 mM, respectively. [10][11][12][13] After oral administration of APV, SQV or NFV with IDV, their AUC values in the presence of IDV were increased 1.6-, 9.5-and 2.3-fold, respectively, compared with any of them alone. On the other hand, the AUC values of APV, SQV and NFV after intravenous co-administration with IDV increased by 1.4-, 1.2-and 1.5-fold, respectively, and showed no notable increase compared to those obtained from oral administration.…”

“…[7][8][9] According to the previous studies, the degrees of in vivo pharmacokinetic interaction between any combination of two drugs selected out of the above five were highly variable. [10][11][12] Even though IDV had the strongest inhibitory effect on APV metabolism in rat liver microsomes, the in vivo effects of an HIV PI after co-administration with IDV could not always be predicted from in vitro results, suggesting the presence of another interaction process besides metabolism in the liver. 13) It has been suggested that in some drugs the role of intestinal metabolism is greater than that of hepatic metabolism in the overall first-pass effect.…”