A series of dipyridodiazepinones have been shown to be potent inhibitors of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase. The lead compound, BI-RG-587, had a 50% inhibitory concentration of 84 nM against HIV-1 reverse transcriptase activity. This compound reduced plaque formation of HIV-1 in HeLa cells expressing the CD4 receptor by 50% at 15 nM. BI-RG-587 at comparable concentrations inhibited the production of p24 antigen following the acute infection of CEM T-lymphoblastoid cells or primary human monocyte-derived macrophages with HIV-1. No inhibitory effects against HIV-2 or against three picornaviruses were detected. Zidovudine (3'-azido-3'-deoxythymidine [AZT])-susceptible and AZT-resistant isolates of HIV-1 were equally susceptible to BI-RG-587. AZT and BI-RG-587 exhibited synergistic inhibition of HIV-1BRU at all concentrations examined.

The effects of tipranavir/ritonavir (TPV/r) on hepatic and intestinal P-glycoprotein (P-gp) and cytochrome P450 (CYP) enzyme activity were evaluated in 23 volunteers. The subjects received oral (p.o.) caffeine, warfarin + vitamin K, omeprazole, dextromethorphan, and midazolam and digoxin (p.o. and intravenous (i.v.)) at baseline, during the first three doses of TPV/r (500 mg/200 mg b.i.d.), and at steady state. Plasma area under the curve (AUC) 0-∞ and urinary metabolite ratios were used for quantification of protein activities. A single dose of TPV/r had no effect on the activity of CYP1A2 and CYP2C9; it weakly inhibited CYP2C19 and P-gp; and it potently inhibited CYP2D6 and CYP3A. Multiple dosing produced weak induction of CYP1A2, moderate induction of CYP2C19, potent induction of intestinal P-gp, and potent inhibition of CYP2D6 and CYP3A, with no significant effects on CYP2C9 and hepatic P-gp. Several P450/transporter single-nucleotide polymorphisms correlated with the baseline phenotype but not with the extent of inhibition or induction. Although mixed induction and inhibition are present, this approach offers an understanding of drug interaction mechanisms and ultimately assists in optimizing the clinical use of TPV/r.Cocktail phenotyping involves simultaneous, single-dose administration of marketed drugs (also known as probes) to measure the activity (or phenotype) of multiple hepatic and intestinal drug-metabolizing enzymes and transporters for rapid and efficient assessment of the drug interaction potential of a new compound. [1][2][3][4][5] The "Cooperstown 5 + 1 cocktail" consists of caffeine, warfarin, omeprazole, dextromethorphan, intravenous (i.v.) midazolam, and vitamin K (to negate warfarin's anticoagulant effect). 6 We have modified this approach to elucidate the specific influences of drugs on hepatic and intestinal proteins by evaluating enzyme activity NIH Public Access Author ManuscriptClin Pharmacol Ther. Author manuscript; available in PMC 2011 June 1. Published in final edited form as:Clin Pharmacol Ther. 2010 June ; 87(6): 735-742. doi:10.1038/clpt.2009.253. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript under baseline conditions in addition to conditions of both acute and chronic drug exposure. Oral (p.o.) midazolam and i.v. and p.o. digoxin were also added as probe substrates in order to measure hepatic + intestinal CYP3A activity, hepatic P-glycoprotein (P-gp) activity, and hepatic + intestinal P-gp activity, respectively. 7,8 The genotyping of cytochrome P450 (CYP) genes corresponding to enzymes investigated with phenotype probes (CYP1A2, CYP2C9, CYP2C19, CYP2D6, and CYP3A4/5/7/43) and P-gp (ABCB1) also allows for investigating genotype-phenotype correlations and determining genetic influences on drug interactions.We used this modified cocktail approach to investigate the drug interaction potential of tipranavir (TPV) administered along with low-dose ritonavir (RTV). TPV is a nonpeptidic protease inhibitor (PI) with potent activity against HIV-1-res...

The results of two randomized, single‐dose, crossover bioavailability studies are presented which describe the pharmacokinetics and oral bioavailability of nevirapine, a novel nonnucleoside antiretroviral drug. In the first study 12 healthy male volunteers received nevirapine 15 mg via short‐term i.v. infusion or orally as a 50 mg tablet or reference solution (50 mg/200 mL). Following the i.v. dose, nevirapine had a low systemic clearance (Mean±S.D., Cl=1.4±0.3 L/h) and a prolonged elimination phase (t1/2β=52.8±14.8 h; MRT=81.4±22.4 h). Nevirapine absolute bioavailability was 93±9% and 91±8% for the tablet and oral solution, respectively. In the second study, 24 healthy male volunteers were administered nevirapine as a 200 mg production‐line tablet or oral reference solution (200 mg/200 mL). There was no significant difference in bioavailability between the tablet and reference solution. Overall, comparison of the pharmacokinetic parameters between the 50 and 200 mg doses indicates that nevirapine is well absorbed at clinically relevant doses. The absorption profiles using deconvolution revealed no evidence of differential enzyme induction between the two doses or routes of administration following a single dose. Copyright © 1999 John Wiley & Sons, Ltd.

Loperamide (LOP) is a peripherally acting opioid receptor agonist used for the management of chronic diarrhea through the reduction of gut motility. The lack of central opioid effects is partly due to the efflux activity of the multidrug resistance transporter P-glycoprotein (P-gp) at the blood-brain barrier. The protease inhibitors are substrates for P-gp and have the potential to cause increased LOP levels in the brain. Because protease inhibitors, including tipranavir (TPV), are often associated with diarrhea, they are commonly used in combination with LOP. The level of respiratory depression, the level of pupil constriction, the pharmacokinetics, and the safety of LOP alone compared with those of LOP-ritonavir (RTV), LOP-TPV, and LOP-TPV-RTV were evaluated in a randomized, open-label, parallel-group study with 24 healthy human immunodeficiency virus type 1-negative adults. Respiratory depression was assessed by determination of the ventilatory response to carbon dioxide. Tipranavir-containing regimens (LOP-TPV and LOP-TPV-RTV) caused decreases in the area under the concentration-time curve from time zero to infinity for LOP (51% and 63% decreases, respectively) and its metabolite (72% and 77% decreases, respectively), whereas RTV caused increases in the levels of exposure of LOP (121% increase) and its metabolite (44% increase). In vitro and in vivo data suggest that TPV is a substrate for and an inducer of P-gp activity. The respiratory response to LOP in combination with TPV and/or RTV was not different from that to LOP alone. There was no evidence that LOP had opioid effects in the central nervous system, as measured indirectly by CO 2 response curves and pupillary response in the presence of TPV and/or RTV.Loperamide (LOP; Imodium, McNeil-PPC, Inc.) is a peripherally acting opioid receptor agonist that reduces gut motility and that is used for the management of chronic diarrhea (8,25). The principal metabolic fate of loperamide in humans involves oxidative N-dealkylation to N-demethyl-loperamide as the principal metabolite. In human liver microsomes, cytochrome P450 3A4 (CYP3A4) appears to be the major isozyme responsible for loperamide metabolism, with minor contributions from CYP2B6 (9). At the doses used to control diarrhea, LOP has very poor penetration of the blood-brain barrier and produces no central opioid effects, such as respiratory depression, pupillary constrictions, analgesia, or changes in alertness (26). The poor central nervous system (CNS) penetration is attributed both to LOP active cellular efflux via the multidrug resistance transporter P-glycoprotein (P-gp) in the blood-brain barrier and to low systemic oral bioavailability (24). When P-gp is inhibited, LOP and its metabolites may potentially enter the brain and cause opioid-induced central neurological adverse events (AEs) (23, 24).Current treatment for human immunodeficiency virus type 1 (HIV-1) infection consists of a combination of antiretroviral agents of different classes. Tipranavir (TPV) is a potent nonpeptidic HIV-1 and HIV-...

This phase 1 study demonstrated that RTV-boosted TPV achieves concentrations that are expected to be effective in treating drug-experienced patients.

To identify pharmacokinetic (PK) drug-drug interactions between tipranavir-ritonavir (TPVTipranavir coadministered with low-dose ritonavir (TPV/r) is an effective treatment option in treatment-experienced human immunodeficiency virus (HIV)-infected patients with resistance to more than one protease inhibitor (PI) (9). TPV/r is associated with adverse effects (AEs) that include increased triglycerides and cholesterol. NIAID Division of AIDS (DAIDS) grade 3 to 4 cholesterol elevation (Ͼ400 mg/dl) and grade 3 to 4 triglyceride elevation (Ͼ750 mg/dl) were higher in the TPV/r-treated patients than in the comparator-boosted PI-treated patients in phase III studies (9). Grade 3 to 4 cholesterol elevation was 4.3 versus 0.6/100 patient exposure years, and triglyceride elevation was 27.8 versus 21.6/100 patient exposure years in the TPV/r versus comparator-boosted PI- (1); however, their use in HIV-infected patients may be limited by clinically significant drug-drug interactions with PIs (5). Atorvastatin is metabolized extensively by cytochrome P450 3A4 (CYP3A4) to metabolites that have in vitro inhibitory activity for HMG-CoA reductase similar to that of atorvastatin. Approximately 70% of the circulating inhibitory activity for HMG-CoA reductase has been attributed to these active metabolites (15). Since TPV/r has a net inhibitory effect on CYP3A4

Celery (Apium graveolens) and parsley (Petroselinum sativum), plants used worldwide in human nutrition, are the natural sources of methoxsalen. In this study we investigated the effect of mice pretreatment with juices of this plants on the hypnotic action of pentobarbital and analgesic action of paracetamol and aminopyrine, the drugs involving cytochrome P450 superfamily in their metabolism. In mice pretreated with celery and parsley juices a prolonged action of pentobarbital with respect to control was observed, statistical significance being attained only with parsley-pretreated animals. Both pretreatments increased and prolonged the analgesic action of aminopyrine and paracetamol, pretreatment with parsley being again more effective. Celery and parsley juices given to animals two hours before their decapitation caused a significant decrease of cytochrome P450 in the liver homogenate as compared to control.

The drug-drug interaction (DDI) potential of deleobuvir, an hepatitis C virus (HCV) polymerase inhibitor, and its two major metabolites, CD 6168 (formed via reduction by gut bacteria) and deleobuvir-acyl glucuronide (AG), was assessed in vitro. Area-under-the-curve (AUC) ratios (AUCi/AUC) were predicted using a static model and compared with actual AUC ratios for probe substrates in a P450 cocktail of caffeine (CYP1A2), tolbutamide (CYP2C9), and midazolam (CYP3A4), administered before and after 8 days of deleobuvir administration to HCV-infected patients. In vitro studies assessed inhibition, inactivation and induction of P450s. Induction was assessed in a short-incubation (10 hours) hepatocyte assay, validated using positive controls, to circumvent cytotoxicity seen with deleobuvir and its metabolites. Overall, P450 isoforms were differentially affected by deleobuvir and its two metabolites. Of note was more potent CYP2C8 inactivation by deleobuvir-AG than deleobuvir and P450 induction by CD 6168 but not by deleobuvir. The predicted net AUC ratios for probe substrates were 2.92 (CYP1A2), 0.45 (CYP2C9), and 0.97 (CYP3A4) compared with clinically observed ratios of 1.64 (CYP1A2), 0.86 (CYP2C9), and 1.23 (CYP3A4). Predictions of DDI using deleobuvir alone would have significantly over-predicted the DDI potential for CYP3A4 inhibition (AUC ratio of 6.15). Including metabolite data brought the predicted net effect close to the observed DDI. However, the static model over-predicted the induction of CYP2C9 and inhibition/inactivation of CYP1A2. This multiple-perpetrator DDI scenario highlights the application of the static model for predicting complex DDI for CYP3A4 and exemplifies the importance of including key metabolites in an overall DDI assessment.