Induction effects of ritonavir: implications for drug interactions

Chronic Effects of Ethanol and/or Darunavir/Ritonavir on U937 Monocytic Cells: Regulation of Cytochrome P450 and Antioxidant Enzymes, Oxidative Stress, and Cytotoxicity

BACKGROUND

Our recent study has shown that acute treatment with ethanol (EtOH) increases oxidative stress and cytotoxicity through cytochrome P450 2E1 (CYP2E1)-mediated pathway in U937 monocytic cells. U937 cells are derived from blood monocytes and are considered as the model system for HIV-related study. Since the prevalence of alcohol use in HIV-infected population is high, and HIV+ patients are on antiretroviral therapy (ART) soon after they are diagnosed, it is important to study the interactions between EtOH and ART in monocytes.

METHODS

This study examined the chronic effects of EtOH and ART (darunavir/ritonavir), alone and in combination, on expression/levels of cytochrome P450 enzymes (CYPs), antioxidant enzymes (AOEs), reactive oxygen species (ROS), and cytotoxicity in U937 cells. The mRNA and protein levels were measured using quantitative reverse transcription polymerase chain reaction and Western blot, respectively. ROS and cytotoxicity were measured using flow cytometry and cell viability assay, respectively.

RESULTS

While chronic ART treatment increased CYP2E1 protein expression by 2-fold, EtOH and EtOH+ART increased CYP2E1 by ~5-fold. In contrast, ART and EtOH treatments decreased CYP3A4 protein expression by 38 ± 17% and 74 ± 15%, respectively, and the combination additively decreased CYP3A4 level by 90 ± 8%. Expressions of superoxide dismutase 1 (SOD1) and peroxiredoxin (PRDX6) were decreased by both EtOH and ART, however, the expressions of SOD2 and catalase were unaltered. These results suggested increased EtOH metabolism, increased ART accumulation, and decreased defense against ROS. Therefore, we determined the effects of EtOH and ART on ROS and cytotoxicity. While ART showed a slight increase, EtOH and EtOH+ART displayed significant increase in ROS and cytotoxicity. Moreover, the combination showed additive effects on ROS and cytotoxicity.

CONCLUSIONS

These results suggest that chronic EtOH, in the absence and presence of ART, increases ROS and cytotoxicity in monocytes, perhaps via CYP- and AOE-mediated pathways. This study has clinical implications in HIV+ alcohol users who are on ART.

Effect of co-medications on paritaprevir, ritonavir, ombitasvir, dasabuvir and ribavirin pharmacokinetics: analysis of data from seven Phase II/III trials

BACKGROUND

The three drug direct-acting antiviral regimen (3D regimen) of ombitasvir, paritaprevir/ritonavir and dasabuvir, with and without ribavirin, was evaluated in one Phase II trial and six Phase III trials in over 2,300 HCV genotype-1-infected patients. Patients continued taking their protocol-permitted co-medications while receiving the 3D ± ribavirin regimen. The effects of the co-medications on exposures of the 3D regimen and ribavirin were examined.

METHODS

Population pharmacokinetic model-predicted steady-state area under the curve (AUC_24,ss) values were evaluated in the presence/absence of the co-medications. Interactions resulting in a greater than 50% reduction or 100% increase in an AUC_24,ss value were examined as covariates for an effect on apparent clearance (CL/F).

RESULTS

More than 1,200 co-medications belonging to 15 drug classes and/or 19 enzyme and transporter inhibitor and/or inducer categories were used concomitantly with the 3D regimen in the trials. Approximately 1,500 patients (65%) in Phase III trials received two or more co-medications from multiple drug classes or categories. No co-medication class/category decreased or increased ombitasvir, dasabuvir, ritonavir or ribavirin AUC_24,ss by more than half or twofold, respectively. Opioids, antipsychotics, anti-epileptics, antidiabetics and non-ethinyl estradiol-containing hormone replacement therapies appeared to have an effect (AUC_24,ss ratio ≤0.5 or ≥2.0) on paritaprevir exposures. However, when these classes were included in the paritaprevir population pharmacokinetic model, only opioids and antidiabetics had a statistically significant effect on CL/F, but with no clinically meaningful increase in exposures (≤55%).

CONCLUSIONS

No dose adjustment is necessary for the 3D ± ribavirin regimen when used with the co-medications included in this analysis as there were no clinically meaningful effects on exposures of the DAAs.

Evaluation of a Potential Interaction Between New Regimens to Treat Hepatitis C and Warfarin

OBJECTIVE

New regimens to treat hepatitis C virus infection have expanded the eligible patient population to include more patients receiving concurrent warfarin. The primary objective of this study was to assess whether a drug interaction occurs when these regimens are added to warfarin therapy.

METHODS

This was a retrospective cohort design using a nationwide database of the Veterans Affairs Health System. Patients on warfarin therapy treated with sofosbuvir or ombitasvir, paritaprevir-ritonavir, and dasabuvir (OBV-PTV/r-DSV) from March 2014 through October 2015 were identified. The warfarin dose response was calculated using a warfarin sensitivity index (WSI) defined as the steady-state INR divided by the mean daily warfarin dose. The primary outcome was the change in WSI from hepatitis C treatment initiation to completion.

RESULTS

The final sample consisted of 271 patients. The WSI decreased 23% from a mean baseline value of 0.53 to 0.39 (decrease of 0.14; 95% CI = 0.11 to 0.16; P < 0.001). OBV-PTV/r-DSV produced a significantly greater decrease than any sofosbuvir regimen. Concurrent ribavirin accounted for an additional decrease in warfarin sensitivity of -0.09 (95% CI = -0.06 to -0.12; P < 0.001). The percentage of subtherapeutic INR results increased from 26% prior to hepatitis C treatment to 58% during treatment.

CONCLUSIONS

Results indicate a clinically significant reduction in warfarin dose-response when hepatitis C treatment regimens were added to warfarin. They were most profound with OBV-PTV/r-DSV. Ribavirin was associated with an additive effect. Clinicians should be aware of this potential drug interaction to closely monitor and minimize subtherapeutic levels of anticoagulation.

Pharmacokinetic Interaction Between Isavuconazole and a Fixed-Dose Combination of Lopinavir 400 mg/Ritonavir 100 mg in Healthy Subjects

This phase 1, open‐label study evaluated the pharmacokinetic effects of coadministration of the antifungal agent, isavuconazole (administered as its water‐soluble prodrug isavuconazonium sulfate), with the antiretroviral agent lopinavir/ritonavir in healthy adults. In part 1, 13 subjects were randomized to 2 arms to receive multiple doses of oral isavuconazole 100 mg either alone or with lopinavir/ritonavir 400/100 mg. In part 2, a different group of 55 subjects were randomized to 3 arms to receive multiple doses of oral isavuconazole 200 mg, either alone or with lopinavir/ritonavir 400/100 mg, or to receive oral lopinavir/ritonavir 400/100 mg alone. Mean area under the concentration‐time curve (AUC) following the last dose (AUC_τ) and C_max of isavuconazole increased by 113% and 96% in part 1 and by 96% and 74% in part 2 in the presence vs absence of lopinavir/ritonavir, respectively. Mean AUC_τ and C_max of lopinavir were 27% and 23% lower, and mean AUC_τ and C_max of ritonavir were 31% and 33% lower in the presence vs absence of isavuconazole, respectively. Mild to moderate gastrointestinal disorders were the most common adverse events experienced. These findings indicate that coadministration of lopinavir/ritonavir with isavuconazole can decrease the exposure of lopinavir/ritonavir and increase the exposure of isavuconazole. Patients should be monitored for reduced antiviral efficacy if these agents are coadministered.

Drug interactions between antiretrovirals and drugs used to treat benign prostatic hyperplasia/lower urinary tract symptoms

INTRODUCTION

Significant advances in antiretroviral (ARV) therapy have transformed HIV into a chronic manageable disease. Co-morbidities associated with aging, such as benign prostatic hyperplasia (BPH), are becoming increasingly prevalent in the HIV-infected population. The pharmacological treatment of BPH involves medications mainly metabolized by CYP 450 enzymes, while many ARVs have inducing or inhibiting effects on the CYP 450 system. Consequently, there is potential for significant pharmacokinetic (PK) interactions between these two classes of medications.

AREAS COVERED

This article reviews the pharmacology and metabolism of selected BPH drug therapies and ARVs, in addition to highlighting potential interactions between these two drug categories. The authors also present PK evidence of interactions from available clinical trials, product monographs and international conference abstracts. Potentially significant drug interactions are summarized and strategies for management are discussed.

EXPERT OPINION

Drugs most likely to interact with BPH medications include protease inhibitors, the non-nucleoside reverse transcriptase inhibitors efavirenz, nevirapine, etravirine, and the cobicistat-boosted integrase inhibitor elvitegravir. Clinically significant PK interactions with BPH medications and dolutegravir, raltegravir, rilpivirine, or the investigational agent doravirine do not appear to exist. Clinicians working with HIV-infected individuals need to recognize the potential for interactions involving BPH and ARV treatments to ensure effective and safe drug therapy use.

A case of a probable drug interaction between lurasidone and atazanavir-based antiretroviral therapy

The cytochrome P450 isoform that is primarily involved in the metabolism of the antipsychotic lurasidone is CYP3A4. Drugs that inhibit or induce this enzyme would then be expected to increase or decrease serum concentrations of lurasidone, respectively. Atazanavir, an HIV-1 protease inhibitor, has demonstrated to be an inhibitor of CYP3A4 and would be expected to increase the exposure of any drug metabolized by this enzyme. We report a case of an atazanavir-precipitated drug-drug interaction that led to elevated serum concentrations of lurasidone and associated clinical symptoms of drug toxicity.

Darunavir/cobicistat once daily for the treatment of HIV

A current focus in HIV management is improving adherence by minimizing pill burden with convenient formulations, including fixed-dose combinations (FDCs). Darunavir, a HIV protease inhibitor, co-administered with low-dose ritonavir (800/100 mg once daily), is recommended in guidelines in combination with other antiretrovirals for HIV patients with no darunavir resistance-associated mutations. Cobicistat is an alternative agent to ritonavir for boosting plasma drug levels of darunavir among other antiretrovirals. Cobicistat is a more specific cytochrome P450 3A inhibitor than ritonavir without enzyme-inducing properties. This review describes the differing effects of cobicistat and ritonavir on metabolic enzymes, which explains their differing drug-drug interactions, and summarizes some of the studied drug-drug interactions for cobicistat. It also outlines the clinical development and data for a once-daily darunavir/cobicistat FDC. This FDC thus allows for a once-daily treatment regimen (including background antiretrovirals) with reduced pill burden.

Ritonavir Use in Human Immunodeficiency Virus-Positive Surgical Patients Is Not Associated with an Increase in Postoperative Critical Respiratory Events

This study evaluated whether highly active antiretroviral therapy for human immunodeficiency virus (HIV) including ritonavir is independently associated with increased critical respiratory events after general anesthesia with opioid analgesia. The impact of ritonavir on hepatic microsomal enzymes was considered due to the effect of these enzymes on opioid metabolism. Medical records of over 1900 patients were reviewed, and those of 941 patients met inclusion criteria and were analyzed. Chronic treatment with ritonavir was not associated with critical respiratory events in HIV-positive patients.

Drug-Drug Interaction of Omeprazole With the HCV Direct-Acting Antiviral Agents Paritaprevir/Ritonavir and Ombitasvir With and Without Dasabuvir

Paritaprevir (administered with low-dose ritonavir), ombitasvir, and dasabuvir are direct-acting antiviral agents administered as combination regimens for the treatment of chronic hepatitis C virus infection. Drug-drug interactions between 2D (ombitasvir/paritaprevir/ritonavir) or 3D (ombitasvir/paritaprevir/ritonavir and dasabuvir) regimens and omeprazole, a CYP2C19 substrate and acid-reducing agent, were evaluated in 24 healthy volunteers. Subjects received omeprazole (40 mg once daily) on day 1 and days 20-24 and the 2D or 3D regimen (ombitasvir/paritaprevir/ritonavir 25/150/100 mg once daily ± dasabuvir 250 mg twice daily) on days 6-24. Compared with omeprazole alone, coadministration with the 2D or 3D regimen decreased omeprazole geometric mean Cmax and AUCt values by 40% to 50%. Ombitasvir, dasabuvir, and ritonavir mean exposures showed <10% change, and paritaprevir mean exposures showed <20% change when the 2D or 3D regimen was administered with omeprazole compared with administration without omeprazole. Although no a priori dose adjustment is needed, a higher omeprazole dose should be considered if clinically indicated when coadministered with the 2D or 3D regimen. No dose adjustment is required for the 2D or 3D regimen when administered with omeprazole, other acid-reducing agents, or CYP2C19 inhibitors.

Pharmacokinetic interactions between artesunate-mefloquine and ritonavir-boosted lopinavir in healthy Thai adults

Background

Concomitant use of anti-malarial and antiretroviral drugs is increasingly frequent in malaria and HIV endemic regions. The aim of the study was to investigate the pharmacokinetic interaction between the anti-malarial drugs, artesunate-mefloquine and the antiretroviral drug, lopinavir boosted with ritonavir (LPV/r).

Methods

The study was an open-label, three-way, sequential, cross-over, pharmacokinetic study in healthy Thai adults. Subjects received the following treatments: Period 1: standard 3-day artesunate-mefloquine combination; Period 2 (2 months wash-out): oral LPV/r 400 mg/100 mg twice a day for 14 days; and, Period 3: artesunate-mefloquine and LPV/r twice a day for 3 days. Sixteen subjects (eight females) were enrolled and pharmacokinetic parameters were determined by non-compartmental analysis.

Results

In the presence of LPV/r, artesunate C_max and systemic exposure were significantly increased by 45–80 %, while the metabolic ratio of dihydroartemisinin to artesunate was significantly reduced by 72 %. In addition, mefloquine C_max and systemic exposure were significantly reduced by 19–37 %. In the presence of artesunate-mefloquine, lopinavir C_max was significantly reduced by 22 % but without significant change in systemic drug exposure. The 90 % CI of the geometric mean ratio (GMR) of AUC_0−∞ and C_max were outside the acceptable bioequivalent range for each drug. Drug treatments were generally well tolerated with no serious adverse events. Vertigo, nausea and vomiting were the most common adverse events reported.

Conclusion

The reduction in systemic exposure of all investigated drugs raises concerns of an increased risk of treatment failure rate in co-infected patients and should be further investigated.

Pharmacokinetic Interactions Between Quinine and Lopinavir/Ritonavir in Healthy Thai Adults

This study aimed to investigate the pharmacokinetic interactions between quinine and lopinavir boosted with ritonavir (LPV/r) in healthy Thai adults (8 males and 12 females). Period 1 (day 1): subjects received a single oral dose of 600 mg quinine sulfate. Period 2: subjects received LPV/r (400/100 mg) twice daily. Period 3: subjects received a single quinine sulfate dose plus LPV/r twice a day. Intensive blood sampling was performed during each phase. Quinine AUC0-48h (area under the plasma concentration-time curve from time 0 to 48 hours), AUC0-∞ (area under the plasma concentration-time curve from time 0 to infinity), and Cmax (maximum concentration over the time-span specified), were 56%, 57%, and 47% lower, respectively, in the presence of LPV/r. 3-Hydroxyquinine AUC0-48h, AUC0-∞, and Cmax were significantly lower and the metabolite-to-parent ratio was significantly reduced. Lopinavir and ritonavir exposures were not significantly reduced with quinine coadministration, but Cmax of both drugs were significantly lower. The geometric mean ratio (GMR) and 90% CI of AUC0-48h, AUC0-∞, and Cmax for quinine, 3-hydroxyquinine, lopinavir, and ritonavir lay outside the bioequivalent range of 0.8-1.25. Drug treatments during all periods were generally well tolerated. The reduction in systemic exposure of quinine and 3-hydroxyquinine with concomitant LPV/r use raises concerns of suboptimal exposure. Studies in HIV/malaria coinfection patients are needed to determine the clinical impact to decide if any change to the quinine dose is warranted.

Pharmacokinetic and pharmacodynamic drug interactions between antiretrovirals and oral contraceptives

More than 50 % of women living with HIV in low- and middle-income countries are of reproductive age, but there are limitations to the administration of oral contraception for HIV-infected women receiving antiretroviral therapy due to drug-drug interactions caused by metabolism via the cytochrome P450 isoenzymes and glucuronidation. However, with the development of newer antiretrovirals that use alternative metabolic pathways, options for contraception in HIV-positive women are increasing. This paper aims to review the literature on the pharmacokinetics and pharmacodynamics of oral hormonal contraceptives when given with antiretroviral agents, including those currently used in developed countries, older ones that might still be used in salvage regimens, or those used in resource-limited settings, as well as newer drugs. Nucleos(t)ide reverse transcriptase inhibitors (NRTIs), the usual backbone to most combined antiretroviral treatments (cARTs) are characterised by a low potential for drug-drug interactions with oral contraceptives. On the other hand non-NRTIs (NNRTIs) and protease inhibitors (PIs) may interact with oral contraceptives. Of the NNRTIs, efavirenz and nevirapine have been demonstrated to cause drug-drug interactions; however, etravirine and rilpivirine appear safe to use without dose adjustment. PIs boosted with ritonavir are not recommended to be used with oral contraceptives, with the exception of boosted atazanavir which should be used with doses of at least 35 µg of estrogen. Maraviroc, an entry inhibitor, is safe for co-administration with oral contraceptives, as are the integrase inhibitors (INIs) raltegravir and dolutegravir. However, the INI elvitegravir, which is given in combination with cobicistat, requires a dose of estrogen of at least 30 µg. Despite the growing evidence in this field, data are still lacking in terms of large cohort studies, randomised trials and correlations to real clinical outcomes, such as pregnancy rates, in women on antiretrovirals and hormonal contraception.

Effect of lopinavir/ritonavir on the pharmacokinetics of selexipag an oral prostacyclin receptor agonist and its active metabolite in healthy subjects

AIMS

This study investigated the effect of a fixed dose combination of lopinavir/ritonavir on the pharmacokinetics (PK) of selexipag and its active metabolite ACT-333679.

METHODS

This was an open label, randomized, single centre, two way, crossover study. Twenty healthy male subjects were treated with a single dose of 400 µg selexipag alone and in combination with multiple doses of lopinavir/ritonavir (400/100 mg) twice daily.

RESULTS

The results showed that lopinavir/ritonavir approximately doubled the exposure to selexipag. The area under the plasma concentration-time curve from time zero to infinity (AUC(0,∞) and the maximum plasma concentration (Cmax) of selexipag were 2.2- and 2.1-fold higher, respectively, than under selexipag alone, with a 90% confidence interval (CI) of the geometric mean ratio (GMR) of 1.9, 2.7 and 1.7, 2.6, respectively. For ACT-333679, the clinically more relevant component of selexipag, systemic exposure was increased by 8% (GMR of AUC(0,∞) 1.1, 90% CI 0.9, 1.3), when lopinavir/ritonavir was co-administered with selexipag. The most frequently reported adverse event (AE) was headache. A single dose of selexipag, administered either alone or together with multiple doses of lopinavir/ritonavir, was safe and well tolerated.

CONCLUSIONS

Lopinavir/ritonavir does not affect the PK parameters of selexipag and ACT-333679 to a clinically relevant extent. Therefore, adaptation of the selexipag dose is not required when co-administered with inhibitors of the organic anion-transporting polypeptide (OATP) 1B1/ 1B3, P-glycoprotein (P-gp) and/or CYP3A4.

Influence of HIV antiretrovirals on methadone N-demethylation and transport

Drug interactions involving methadone and/or HIV antiretrovirals can be problematic. Mechanisms whereby antiretrovirals induce clinical methadone clearance are poorly understood. Methadone is N-demethylated to 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) by CYP2B6 and CYP3A4 in vitro, but by CYP2B6 in vivo. This investigation evaluated human hepatocytes as a model for methadone induction, and tested the hypothesis that methadone and EDDP are substrates for human drug transporters. Human hepatocyte induction by several antiretrovirals of methadone N-demethylation, and CYP2B6 and CYP3A4 transcription, protein expression and catalytic activity, and pregnane X receptor (PXR) activation were evaluated. Methadone and EDDP uptake and efflux by overexpressed transporters were also determined. Methadone N-demethylation was generally not significantly increased by the antiretrovirals. CYP2B6 mRNA and activity (bupropion N-demethylation) were induced by several antiretrovirals, as were CYP3A4 mRNA and protein expression, but only indinavir increased CYP3A activity (alfentanil dealkylation). CYP upregulation appeared related to PXR activation. Methadone was not a substrate for uptake (OCT1, OCT2, OCT3, OATP1A2, OATP1B1, OATP1B3, OATP2B1) or efflux (P-gp, BCRP) transporters. EDDP was a good substrate for P-gp, BCRP, OCT1, OCT3, OATP1A2, and OATP1B1. OATP1A2- and OCT3-mediated EDDP uptake, and BCRP-mediated EDDP efflux transport, was inhibited by several antiretrovirals. Results show that hepatocyte methadone N-demethylation resembles expressed and liver microsomal metabolism more than clinical metabolism. Compared with clinical studies, hepatocytes underreport induction of methadone metabolism by HIV drugs. Hepatocytes are not a good predictive model for clinical antiretroviral induction of methadone metabolism and not a substitute for clinical studies. EDDP is a transporter substrate, and is susceptible to transporter-mediated interactions.

Drug Interactions With Direct-Acting Antivirals for Hepatitis C: Implications for HIV and Transplant Patients

OBJECTIVE

Review pharmacokinetics of new direct-acting antivirals (DAAs) for hepatitis C (HCV) infection and interactions with concomitant immunosuppressant and antiretroviral therapies (ART).

DATA SOURCES

MEDLINE (1948-January 2015), EMBASE (1964-January 2015), International Pharmaceutical Abstracts (1970-January 2015), Google, and Google Scholar were searched combining the terms simeprevir, sofosbuvir, ledipasvir, daclatasvir, paritaprevir, ABT-450, ombitasvir, dasabuvir, pharmacokinetics, drug interaction, drug metabolism, HIV, antiretroviral, immunosuppressant, transplant. Articles, conference proceedings, abstracts, and product monographs were reviewed.

STUDY SELECTION AND DATA EXTRACTION

Literature on pharmacokinetic or pharmacodynamic interactions with DAAs and immunosuppressants or ART was considered for inclusion. Pertinent information was extracted and summarized in the review. In the absence of data, pharmacokinetic and pharmacodynamic principles were used to predict the likelihood of interactions.

DATA SYNTHESIS

DAA pharmacokinetics are reviewed and drug interaction data are presented with provision of management strategies. Fixed-dose combination paritaprevir/ritonavir/ombitasvir plus dasabuvir is most susceptible to drug interactions with immunosuppressants and ART mainly due to the influence of ritonavir on multiple enzymes. Simeprevir is also prone to drug interactions because of cytochrome P450(CYP) 3A4, CYP1A2, P-glycoprotein, and OATP1 involvement and is not recommended for use in combination with several HIV antiretrovirals (ARVs). Close therapeutic drug monitoring of calcineurin inhibitors is required with concomitant simeprevir. Few clinically significant interactions are expected with sofosbuvir or ledipasvir. Limited data suggest that daclatasvir may be coadministered with immunosuppressants but requires dose adjustments with certain ARVs.

CONCLUSIONS

None of the DAAs are completely free of drug interactions. Awareness and management of drug interactions is critical to optimize outcomes and minimize adverse effects in these patient populations.

Cobicistat-boosted darunavir in HIV-1-infected adults: week 48 results of a Phase IIIb, open-label single-arm trial

Background

Cobicistat is an alternative pharmacoenhancer to ritonavir. In healthy volunteers, darunavir exposure was comparable when darunavir 800 mg once daily was co-administered with cobicistat 150 mg once daily (as single agents or a fixed-dose combination) vs. with ritonavir 100 mg once daily.

Methods

This 48-week, Phase IIIb, single-arm, US multicenter study (NCT01440569) evaluated safety, efficacy and pharmacokinetics of darunavir/cobicistat 800/150 mg once daily (as single agents) plus two investigator-selected nucleoside/tide reverse transcriptase inhibitors (N[t]RTIs) in HIV-1-infected adults. Patients had no darunavir resistance-associated mutations (RAMs), plasma viral load (VL) ≥1000 HIV-1 RNA copies/ml, eGFR ≥80 ml/min and genotypic sensitivity to the two N[t]RTIs. The primary endpoint was any treatment-emergent grade 3 or 4 adverse events (AEs) through Week 24.

Results

The majority of the 313 intent-to-treat patients were treatment-naïve (295/313; 94%), male (89%), White (60%) and received a tenofovir-based regimen (99%). Median baseline VL and CD4⁺ count overall were 4.8 log₁₀ HIV-1 RNA copies/ml and 361 cells/mm³, respectively. Overall, 86% of patients (268/313) completed the study. The majority of discontinuations were for AEs (15/313; 5%). The incidence of treatment-emergent grade 3 or 4 AEs regardless of causality was 6% through Week 24 and 8% through Week 48. Most common AEs through Week 48 were diarrhea (27%) and nausea (23%), which were grade 1 or 2 in severity. Week 48 virologic response rates (% with VL <50 HIV-1 RNA copies/ml; Snapshot analysis) were 81% overall and 83% in treatment-naïve patients; median increases in CD4⁺ count at 48 weeks were 167 and 169 cells/mm³, respectively. Of 15/313 patients who met the criteria for resistance analysis, one developed a darunavir RAM as a mixture with wild-type (I84I/V), without phenotypic resistance to darunavir. The mean population pharmacokinetic-derived darunavir areas under the plasma concentration–time curve were 102,000 overall and 100,620 ng•h/ml in treatment-naïve patients. No clinically relevant relationships were seen between darunavir exposure and virologic response, AEs or laboratory parameters.

Conclusion

Darunavir/cobicistat 800/150 mg once daily was generally well tolerated through Week 48, with no new safety concerns. Pharmacokinetics, virologic and immunologic responses for darunavir/cobicistat were similar to previous data for darunavir/ritonavir 800/100 mg once daily.

Effect of fosamprenavir-ritonavir on the pharmacokinetics of dolutegravir in healthy subjects

Dolutegravir (DTG) is an HIV integrase inhibitor (INI) with demonstrated activity in INI-naive and INI-resistant patients. The objective of this open-label, 2-period, single-sequence study was to evaluate the effect of fosamprenavir-ritonavir (FPV-RTV) on the steady-state plasma pharmacokinetics of DTG. Twelve healthy subjects received 50 mg DTG once daily for 5 days (period 1), followed by 10 days of 50 mg DTG once daily in combination with 700/100 mg FPV-RTV every 12 h (period 2). All doses were administered in the fasting state. Serial pharmacokinetic samples for DTG and amprenavir and safety assessments were obtained throughout the study. Noncompartmental pharmacokinetic analysis was performed, and geometric least-squares mean ratios and 90% confidence intervals were generated for within-subject treatment comparison. Fosamprenavir-ritonavir decreased the DTG area under the concentration-time curve, maximum concentration in plasma, and concentration in plasma at the end of the dosing interval by 35%, 24%, and 49%, respectively. Both DTG and DTG with FPV-RTV were well tolerated; no subject withdrew because of adverse events. The most frequently reported drug-related adverse events were rash, abnormal dreams, and nasopharyngitis. The modest decrease in DTG exposure when it was coadministered with FPV-RTV is not considered clinically significant, and DTG dose adjustment is not required with coadministration of FPV-RTV in INI-naive patient populations on the basis of established "no-effect" boundaries of DTG. In the INI-resistant population, as a cautionary measure, alternative combinations that do not include FPV-RTV should be considered. (This study has been registered at ClinicalTrials.gov under identifier NCT01209065.).

A randomized trial in healthy subjects to assess the bioequivalence of an atazanavir/cobicistat fixed-dose combination tablet versus administration as separate agents

BACKGROUND

Cobicistat (COBI) is an alternative pharmacoenhancer to ritonavir. A fixed-dose combination (FDC) tablet containing atazanavir (ATV) and COBI has been developed for the treatment of HIV-1-infected patients.

METHODS

This open-label, single-centre, single-dose, crossover study, randomized 64 healthy subjects to one of eight treatment sequences. Under light meal conditions, maximum plasma concentration (Cmax), area under the plasma concentration-time curve (AUC) to infinity (AUCINF) and AUC to the last measurable concentration (AUC0-T) for ATV and COBI administered as an FDC of ATV/COBI (300/150 mg) were compared to those following administration as separate agents given together; bioequivalence was concluded if the 90% CIs of the geometric mean ratios fell within the predetermined range of 0.80, 1.25. ATV and COBI pharmacokinetic parameters following administration as the FDC or as separate agents were also compared under fasted conditions. The effect of food (light and high-fat meals) on the pharmacokinetics of ATV and COBI for the FDC was also assessed.

RESULTS

ATV and COBI administered in an FDC tablet were bioequivalent to the individual agents when given with a light meal. Under fasted conditions, pharmacokinetic parameters for ATV and COBI were similar for the individual components and the FDC. For the FDC, systemic exposure to ATV increased with a light meal compared to fasted conditions, and ATV concentration 24 h post-dose was similar with a light meal compared with a high-fat meal.

CONCLUSIONS

ATV/COBI (300/150 mg) FDC tablet was bioequivalent to coadministration as separate agents with a light meal in healthy subjects. Clinicaltrials.gov identifier NCT01837719.

Clinical pharmacokinetic drug interactions associated with artemisinin derivatives and HIV-antivirals

Management of HIV and malaria co-infection is challenging due to potential drug-drug interactions between antimalarial and HIV-antiviral drugs. Little is known of the clinical significance of these drug interactions, and this review provides a comprehensive summary and critical evaluation of the literature. Specifically, drug interactions between WHO-recommended artemisinin combination therapies (ACT) and HIV-antivirals are discussed. An extensive literature search produced eight articles detailing n = 44 individual pharmacokinetic interactions. Only data pertaining to artemether-lumefantrine and two other artesunate combinations are available, but most of the interactions are characterized on at least two occasions by two different groups. Overall, protease inhibitors (PIs) tended to increase the exposure of lumefantrine and decrease the exposures of artemether and dihydroartemisinin, a pharmacologically active metabolite of artemether. Non-nucleoside reverse transcriptase inhibitors (NNRTIs) tended to decrease the exposures of artemether, dihydroartemisinin, and lumefantrine when co-administered with artemether-lumefantrine. Fewer studies characterized the effects of PIs or NNRTIs on artesunate combinations, but nevirapine increased artesunate exposure and ritonavir decreased dihydroartemisinin exposure. On the other hand, artemether-lumefantrine or artesunate combinations had little effect on the pharmacokinetics of HIV-antivirals, with the exception of decreased nevirapine exposure from artemether-lumefantrine or increased ritonavir exposure from pyronaridine/artesunate co-administration. In general, pharmacokinetic interactions can be explained by the metabolic properties of the co-administered drugs. Despite several limitations to the studies, these data do provide valuable insights into the potential pharmacokinetic perturbations, and the consistently marked elevation or reduction in ACT exposure in some cases cannot be overlooked.

Pharmacokinetics of darunavir in fixed-dose combination with cobicistat compared with coadministration of darunavir and ritonavir as single agents in healthy volunteers

This study compared the bioavailability of two candidate fixed-dose combinations (FDCs: G003 and G004) of darunavir/cobicistat 800/150 mg with that of darunavir 800 mg and ritonavir 100 mg coadministered as single agents. Short-term safety and tolerability of the FDC formulations were also assessed. This open-label trial included 36 healthy volunteers and assessed steady-state pharmacokinetics of darunavir over 3 randomized, 10-day treatment sequences, under fed conditions. Blood samples for determination of plasma concentrations of darunavir and cobicistat or ritonavir were taken over 24 hours on day 10 and analyzed by liquid-chromatography tandem mass-spectroscopy. Darunavir AUC24h following administration of the FDCs (G003: 74,780 ng ∙ h/mL and G004: 76,490 ng ∙ h/mL) was comparable to that following darunavir/ritonavir (78,410 ng ∙ h/mL), as was Cmax (6,666 and 6,917 ng/mL versus 6,973 ng/mL, respectively). Modestly lower C0h (1,504 and 1,478 ng/mL versus 2,015 ng/mL) and Cmin (1,167 and 1,224 ng/mL versus 1,540 ng/mL) values were seen with the FDCs. Short-term tolerability of the FDCs was comparable to that of darunavir/ritonavir when administered as single agents. The most common adverse events reported were headache, gastrointestinal upset, or rash. Cobicistat is an effective pharmacoenhancer of darunavir when administered as an FDC. Short-term administration of darunavir/ritonavir or darunavir/cobicistat was generally well tolerated.

Antiretrovirals and the kidney in current clinical practice: renal pharmacokinetics, alterations of renal function and renal toxicity

Assessment of renal function in HIV-positive patients is of increasing importance in the context of ageing and associated comorbidities. Exposure to nephrotoxic medications is widespread, and several commonly used antiretroviral drugs have nephrotoxic potential. Moreover, specific antiretrovirals inhibit renal tubular transporters resulting in the potential for drug-drug interactions as well as increases in serum creatinine concentrations, which affect estimates of glomerular filtration rate in the absence of changes in actual glomerular filtration rate. This review explores the effects of antiretroviral therapy on the kidney and offers an understanding of mechanisms that lead to apparent and real changes in renal function.

Structure-activity relationships of diamine inhibitors of cytochrome P450 (CYP) 3A as novel pharmacoenhancers. Part II: P2/P3 region and discovery of cobicistat (GS-9350)

The HIV protease inhibitor (PI) ritonavir (RTV) has been widely used as a pharmacoenhancer for other PIs, which are substrates of cytochrome P450 3A (CYP3A). However the potent anti-HIV activity of ritonavir may limit its use as a pharmacoenhancer with other classes of anti-HIV agents. Ritonavir is also associated with limitations such as poor physicochemical properties. To address these issues a series of compounds with replacements at the P2 and/or P3 region was designed and evaluated as novel CYP3A inhibitors. Through these efforts, a potent and selective inhibitor of CYP3A, GS-9350 (cobicistat) with improved physiochemical properties was discovered.

Structure-activity relationships of diamine inhibitors of cytochrome P450 (CYP) 3A as novel pharmacoenhancers, part I: core region

Ritonavir (RTV), an HIV-1 protease inhibitor (PI), is also a potent mechanism-based inhibitor of human cytochrome P450 3A (CYP3A) and has been widely prescribed as a pharmacoenhancer. As a boosting agent for marketed PIs, it reduces pill burden, and improves compliance. Removal of the hydroxyl group from RTV reduces, but does not eliminate HIV PI activity and does not affect CYP3A inhibition. Herein we report the discovery of a novel series of CYP3A inhibitors that are devoid of antiviral activity. The synthesis and evaluation of analogs with extensive modifications of the 1,4-diamine core along with the structure activity relationships with respect to anti-HIV activity, CYP3A inhibitory activity, selectivity against other CYP enzymes and the human pregnane X receptor (PXR) will be discussed.

Role of ritonavir in the drug interactions between telaprevir and ritonavir-boosted atazanavir

BACKGROUND

Detrimental bidirectional pharmacokinetic interactions have been observed when telaprevir (TVR) and ritonavir (RTV)-boosted human immunodeficiency virus (HIV) protease inhibitors are coadministered in healthy volunteers. Our aim was to evaluate the role of RTV in the bidirectional TVR and atazanavir (ATV) interactions.

METHOD

An open-label, sequential study was carried out in hepatitis C virus (HCV)/HIV-coinfected patients on a RTV-boosted ATV-based (ATVr) antiretroviral regimen (300/100 mg every 24 hours) and triple therapy for chronic C hepatitis genotype 1 (TVR, 1125 mg every 12 hours, pegylated interferon-alpha and ribavirin). Pharmacokinetic profiles were acquired before and after switching from ATVr to unboosted ATV (200 mg every 12 hours). The plasma levels of both drugs were determined by liquid chromatography coupled with mass spectrometry. Pharmacokinetic parameters were calculated by noncompartmental analysis and compared by geometric mean ratios and their 90% confidence intervals.

RESULTS

Fourteen white HCV/HIV-coinfected males were enrolled in this study. After RTV was withdrawn, the TVR AUC(0-12) (area under the concentration-time curve), maximum concentration (C(max)), and minimum concentration (C(min)) values increased by 19% (7%-30%), 12% (0.9%-29%), and 18% (2%-34%), respectively, without any changes in the TVR terminal half-life. The ATV AUC(0-12), C(max), and C(min) values were 39% (13%-66%), 19% (8%-59%), and 48% (1%-96%) higher, respectively, with a significantly shorter terminal half-life (22.6 hours vs 10.4 hours).

CONCLUSIONS

RTV is responsible for the adverse interactions that occur when TVR and ATVr are administered together, possibly by influencing either the absorption phase or first-pass metabolism of TVR. The boost effect of TVR on ATV exposure is higher than on RTV, despite its shorter terminal half-life. The coadministration of TVR and unboosted ATV results in increased exposure of both drugs compared with their coadministration with RTV.

CLINICAL TRIALS REGISTRATION

ClinicalTrials.gov: NCT01818856. European Medicines Agency EudraCT no. 2012-002515-25.

Cytochrome P4503A does not mediate the interaction between methadone and ritonavir-lopinavir

Plasma concentrations of orally administered methadone are reduced by the human immunodeficiency virus protease inhibitor combination ritonavir and lopinavir, but the mechanism is unknown. Methadone metabolism, clearance, and drug interactions have been attributed to CYP3A4, but this remains controversial. This investigation assessed the effects of acute (2 days) and steady-state (2 weeks) ritonavir-lopinavir on intravenous and oral methadone metabolism and clearance, hepatic and intestinal CYP3A4/5 activity (using the probe substrate intravenous and oral alfentanil), and intestinal transporter activity (using oral fexofenadine) in healthy volunteers. Plasma and urine concentrations of methadone and metabolite enantiomers, and other analytes, were determined by mass spectrometry. Acute and chronic ritonavir-lopinavir reduced plasma methadone enantiomer concentrations in half, with an average 2.6- and 1.5-fold induction of systemic and apparent oral methadone clearances. Induction was attributable to stereoselectively increased hepatic methadone N-demethylation, hepatic extraction, and hepatic clearance, and there was a strong correlation between methadone N-demethylation and clearance. Methadone renal clearance was unchanged. Alfentanil's systemic clearance and hepatic extraction, apparent oral clearance, and intestinal extraction were reduced to 25%, 16%, and 35% of control, indicating strong inhibition of hepatic and intestinal CYP3A activities. Ritonavir-lopinavir (acute > chronic) increased fexofenadine exposure, suggesting intestinal P-glycoprotein inhibition. No correlation was found between methadone clearance and CYP3A activity. Acute and steady-state ritonavir-lopinavir stereoselectively induced methadone N-demethylation and clearance, despite significant inhibition of hepatic and intestinal CYP3A activity. Ritonavir-lopinavir inhibited intestinal transporters activity but had no effect on methadone bioavailability. These results do not support a significant role for CYP3A or ritonavir-lopinavir-inhibitable intestinal transporters in single-dose methadone disposition.

Effect of ritonavir-boosted danoprevir, a potent hepatitis C virus protease inhibitor, on the pharmacokinetics of methadone in healthy subjects undergoing methadone maintenance therapy

STUDY OBJECTIVE

To investigate the steady-state pharmacokinetics of methadone when coadministered with ritonavir-boosted danoprevir (DNVr).

DESIGN

Open-label, two-period, single-sequence pharmacokinetic study.

SETTING

Two U.S. research centers.

PATIENTS

Eighteen methadone-maintained healthy adults.

MEASUREMENTS AND MAIN RESULTS

In Period 1 (Day -1), subjects received their daily methadone maintenance therapy (MMT). In Period 2 (Days 1-10), subjects received MMT plus DNVr 100/100 mg twice/day. Pharmacokinetic parameters for the total concentrations of (R)- and (S)-methadone on Days -1 and 10 were determined using noncompartmental methods. Unbound (R)- and (S)-methadone concentrations at 3 hours postdose were also assessed on Days -1 and 10. Geometric mean ratios (GMRs) and 90% confidence intervals (CIs) were used to compare steady-state (R)- and (S)-methadone pharmacokinetics when MMT was administered with or without DNVr. Methadone withdrawal was assessed using the Subjective Opiate Withdrawal Scale. Compared with MMT alone, methadone AUCtau and Cmax GMR (90% CI) following coadministration with DNVr were 1.02 (0.91-1.15) and 1.01 (0.90-1.13) for (R)-methadone, and 1.01 (0.90-1.13) and 0.99 (0.89-1.10) for (S)-methadone, respectively. Unbound (R- and (S)-methadone concentrations were comparable with or without DNVr. No instances of methadone withdrawal were reported. MMT in combination with DNVr was well tolerated.

CONCLUSION

Coadministration of DNVr with MMT resulted in no significant pharmacokinetic interactions or signs of methadone withdrawal. No dosage adjustment is needed for MMT when coadministered with DNVr.

The effect of ritonavir on human CYP2B6 catalytic activity: heme modification contributes to the mechanism-based inactivation of CYP2B6 and CYP3A4 by ritonavir

The mechanism-based inactivation of human CYP2B6 by ritonavir (RTV) in a reconstituted system was investigated. The inactivation is time, concentration, and NADPH dependent and exhibits a K(I) of 0.9 μM, a k(inact) of 0.05 min⁻¹, and a partition ratio of approximately 3. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis showed that the protonated molecular ion of RTV exhibits an m/z at 721 and its two major metabolites are an oxidation product with MH⁺ at m/z 737 and a deacylated product with MH⁺ at m/z 580. Inactivation of CYP2B6 by incubation with 10 μM RTV for 10 min resulted in an approximately 50% loss of catalytic activity and native heme, but no modification of the apoprotein was observed. RTV was found to be a potent mixed-type reversible inhibitor (K(i) = 0.33 μM) and a type II ligand (spectral dissociation constant-K(s) = 0.85 μM) of CYP2B6. Although previous studies have demonstrated that RTV is a potent mechanism-based inactivator of CYP3A4, the molecular mechanism responsible for the inactivation has not been determined. Here, we provide evidence that RTV inactivation of CYP3A4 is due to heme destruction with the formation of a heme-protein adduct. Similar to CYP2B6, there is no significant modification of the apoprotein. Furthermore, LC-MS/MS analysis revealed that both CYP3A4 and human liver microsomes form an RTV-glutathione conjugate having a MH⁺ at m/z 858 during metabolism of RTV, suggesting the formation of an isocyanate intermediate leading to formation of the conjugate.

A randomised study of the effect of danoprevir/ritonavir or ritonavir on substrates of cytochrome P450 (CYP) 3A and 2C9 in chronic hepatitis C patients using a drug cocktail

PURPOSE

The aim of this study was to evaluate the effects of danoprevir in combination with low-dose ritonavir (danoprevir/r) and placebo plus low-dose ritonavir on the pharmacokinetics of probe drugs for cytochrome P450 (CYP) 3A and CYP2C9, in patients with chronic hepatitis C.

METHODS

A total of 54 patients infected with hepatitis C virus genotype 1 received an oral drug cocktail (2 mg midazolam, 10 mg warfarin and 10 mg vitamin K) before and after 14 days of dosing with either danoprevir/r or placebo plus low-dose ritonavir (placebo/r). Serial pharmacokinetic samples were collected up to 24 (midazolam) and 72 (S-warfarin) h post-dose. Plasma concentrations of midazolam, α-hydroxymidazolam and S-warfarin were measured using validated assays. Pharmacokinetic parameters were estimated using non-compartmental analysis, and geometric mean ratios (GMRs) and 90 % confidence intervals (CIs) for the differences between baseline and post-dosing values were calculated.

RESULTS

Danoprevir/r and placebo/r significantly increased midazolam area under the time-concentration curve (AUC0-∞) and reduced the midazolam metabolic ratio while S-warfarin AUC0-∞ was modestly decreased. When danoprevir data were pooled across doses, the midazolam GMR (90 % CI) AUC0-∞ was 9.41 (8.11, 10.9) and 11.14 (9.42, 13.2) following danoprevir/r and placebo/r dosing, respectively, and the S-warfarin GMR (90 % CI) AUC0-∞ was 0.72 (0.68, 0.76) and 0.76 (0.69, 0.85), respectively. The effects of danoprevir/r and placebo/r appeared to be qualitatively similar.

CONCLUSIONS

Substantial inhibition of CYP3A- and modest induction of CYP2C9- activity were observed with danoprevir/r and low-dose ritonavir.

Pyridine-substituted desoxyritonavir is a more potent inhibitor of cytochrome P450 3A4 than ritonavir

Utilization of the cytochrome P450 3A4 (CYP3A4) inhibitor ritonavir as a pharmacoenhancer for anti-HIV drugs revolutionized the treatment of HIV infection. However, owing to ritonavir-related complications, there is a need for development of new CYP3A4 inhibitors with improved pharmacochemical properties, which requires a full understanding of the CYP3A4 inactivation mechanisms and the unraveling of possible inhibitor binding modes. We investigated the mechanism of CYP3A4 interaction with three desoxyritonavir analogues, containing the heme-ligating imidazole, oxazole, or pyridine group instead of the thiazole moiety (compounds 1, 2, and 3, respectively). Our data show that compound 3 is superior to ritonavir in terms of binding affinity and inhibitory potency owing to greater flexibility and the ability to adopt a conformation that minimizes steric clashing and optimizes protein-ligand interactions. Additionally, Ser119 was identified as a key residue assisting binding of ritonavir-like inhibitors, which emphasizes the importance of polar interactions in the CYP3A4-ligand association.

Preclinical pharmacokinetics and tissue distribution of long-acting nanoformulated antiretroviral therapy

Long-acting injectable nanoformulated antiretroviral therapy (nanoART) was developed with the explicit goal of improving medicine compliance and for drug targeting of viral tissue reservoirs. Prior nanoART studies completed in humanized virus-infected mice demonstrated sustained antiretroviral responses. However, the pharmacokinetics (PK) and tissue distribution of nanoART were not characterized. To this end, the PK and tissue distribution of nanoformulated atazanavir (ATV) and ritonavir (RTV) injected subcutaneously or intramuscularly in mice and monkeys were evaluated. Fourteen days after injection, ATV and RTV levels were up to 13-, 41-, and 4,500-fold higher than those resulting from native-drug administration in plasma, tissues, and at the site of injection, respectively. At nanoART doses of 10, 50, 100, and 250 mg/kg of body weight, relationships of more- and less-than-proportional increases in plasma and tissue levels with dose increases were demonstrated with ATV and RTV. Multiple-dose regimens showed serum and tissue concentrations up to 270-fold higher than native-drug concentrations throughout 8 weeks of study. Importantly, nanoART was localized in nonlysosomal compartments in tissue macrophages, creating intracellular depot sites. Reflective data were obtained in representative rhesus macaque studies. We conclude that nanoART demonstrates blood and tissue antiretroviral drug levels that are enhanced compared to those of native drugs. The sustained and enhanced PK profile of nanoART is, at least in part, the result of the sustained release of ATV and RTV from tissue macrophases and at the site of injection.

Cobicistat: a new boost for the treatment of human immunodeficiency virus infection

Ritonavir is commonly used as a pharmacokinetic booster for antiretroviral regimens in the management of human immunodeficiency virus infections. Limitations to ritonavir boosting include increased pill burden, adverse effects, and a wide range of clinically significant drug-drug interactions. Cobicistat is a new pharmacokinetic booster that is a selective inhibitor of cytochrome P450 3A, the main metabolizing pathway of several antiretrovirals. Cobicistat has been studied as a booster for elvitegravir, a second-generation integrase inhibitor, and protease inhibitors. Based on successful clinical trials, a new single-tablet regimen of elvitegravir, cobicistat, emtricitabine, and tenofovir has been approved for the management of treatment-naïve patients. Additional studies are underway investigating the safety and efficacy of cobicistat-boosted protease inhibitor regimens for both treatment-naïve and treatment-experienced patients. Cobicistat is well tolerated and may become a preferred booster for antiretroviral regimens, as it can be coformulated with several agents to create simpler regimens.

Drug interactions between antiretrovirals and hormonal contraceptives

INTRODUCTION

Significant advances in antiretroviral therapy have transformed HIV into a chronic manageable disease, and millions of women living with HIV now have the opportunity to reconsider their reproductive choices, be it contraception or pregnancy planning. Hormonal contraceptives are metabolized by cytochrome P450 isoenzymes and sulfate and glucuronide conjugation in the liver. Many antiretrovirals have inducing or inhibiting effects on the cytochrome P450 system. As such, the pharmacokinetics of hormonal contraceptives can be affected by antiretroviral therapy with potential for significant clinical impact.

AREAS COVERED

This article presents the pharmacology and metabolism of selected antiretrovirals and hormonal contraceptives, and highlights the potential interactions between these two classes of drugs. Furthermore, the authors present the pharmacokinetic evidence of interactions from available clinical trials, product monographs, and international conference abstracts.

EXPERT OPINION

Drugs most likely to interact with combined oral contraceptives, transdermal and implant contraceptives include protease inhibitors, the NNRTIs efavirenz and nevirapine, and cobicistat-boosted elvitegravir. There do not appear to be significant pharmacokinetic interactions with depo-medroxyprogesterone or intrauterine systems and antiretrovirals, although further study is needed. Clinicians working with HIV-positive women need to know the significance of these interactions in order to properly counsel patients and prevent unplanned pregnancies.

Impact of low-dose ritonavir on danoprevir pharmacokinetics: results of computer-based simulations and a clinical drug-drug interaction study

BACKGROUND AND OBJECTIVE

Danoprevir, a potent, selective inhibitor of the hepatitis C virus (HCV) NS3/4A protease, is metabolized by cytochrome P450 (CYP) 3A. Clinical studies in HCV patients have shown a potential need for a high danoprevir daily dose and/or dosing frequency. Ritonavir, an HIV-1 protease inhibitor (PI) and potent CYP3A inhibitor, is used as a pharmacokinetic enhancer at subtherapeutic doses in combination with other HIV PIs. Coadministering danoprevir with ritonavir as a pharmacokinetic enhancer could allow reduced danoprevir doses and/or dosing frequency. Here we evaluate the impact of ritonavir on danoprevir pharmacokinetics.

METHODS

The effects of low-dose ritonavir on danoprevir pharmacokinetics were simulated using Simcyp, a population-based simulator. Following results from this drug-drug interaction (DDI) model, a crossover study was performed in healthy volunteers to investigate the effects of acute and repeat dosing of low-dose ritonavir on danoprevir single-dose pharmacokinetics. Volunteers received a single oral dose of danoprevir 100 mg in a fixed sequence as follows: alone, and on the first day and the last day of 10-day dosing with ritonavir 100 mg every 12 hours.

RESULTS

The initial DDI model predicted that following multiple dosing of ritonavir 100 mg every 12 hours for 10 days, the danoprevir area under the plasma concentration-time curve (AUC) from time zero to 24 hours and maximum plasma drug concentration (C(max)) would increase by about 3.9- and 3.2-fold, respectively. The clinical results at day 10 of ritonavir dosing showed that the plasma drug concentration at 12 hours postdose, AUC from time zero to infinity and C(max) of danoprevir increased by approximately 42-fold, 5.5-fold and 3.2-fold, respectively, compared with danoprevir alone. The DDI model was refined with the clinical data and sensitivity analyses were performed to better understand factors impacting the ritonavir-danoprevir interaction.

CONCLUSION

DDI model simulations predicted that danoprevir exposures could be successfully enhanced with ritonavir coadministration, and that a clinical study confirming this result was warranted. The clinical results demonstrate that low-dose ritonavir enhances the pharmacokinetic profile of low-dose danoprevir such that overall danoprevir exposures can be reduced while sustaining danoprevir trough concentrations.

Tools for eradicating HIV in the brain: prodrug dimeric inhibitors of P-gp

Despite positive developments with the use of combination antiretroviral therapy, a major impediment to limiting the neurocognitive effects of HIV and eradicating HIV brain reservoirs is the penetration of these therapies across the blood-brain barrier (BBB). The focus of our work, therefore, has been to develop tools to significantly improve the penetration of antiretroviral agents to sites of HIV reservoirs, with an emphasis on the CNS. To this end, we have developed an innovative chemical approach--dimeric prodrugs of the antiretroviral agents themselves with a traceless tether. These dimeric prodrugs were designed to serve two purposes: inhibition of P-gp, the major drug efflux protein at the BBB, by occupying two substrate binding sites in the transporter; and prodrug dimers that gain entry into the endothelial cells at the BBB would revert to their monomeric forms in the reducing environment of the cytosol due to breakdown of the traceless tether, thus delivering the therapy. We have demonstrated the feasibility of this design by dimerizing the P-gp substrate and antiviral agent abacavir with a traceless tether. Abacavir dimers displayed potent inhibition of P-gp in two different cellular settings and reverted to active abacavir in the reducing environment of HIV-infected T cells, also leading to antiviral activity. Overall, these experiments point to the excellent promise for future use of dimeric prodrug inhibitors of P-gp for brain penetration of a wide range of CNS-active agents that are substrates of P-gp.

Human immunodeficiency virus protease inhibitors modulate Ca2+ homeostasis and potentiate alcoholic stress and injury in mice and primary mouse and human hepatocytes

A portion of human immunodeficiency virus (HIV)-infected patients undergoing protease inhibitor (PI) therapy concomitantly consume or abuse alcohol leading to hepatic injury. The underling mechanisms are not known. We hypothesize that HIV PIs aggravate alcohol-induced liver injury through an endoplasmic reticulum (ER) stress mechanism. To address this, we treated mice, primary mouse hepatocytes (PMHs), and primary human hepatocytes (PHHs) with alcohol and the HIV PIs ritonavir (RIT) and lopinavir (LOP). In mice, RIT and LOP induced mild ER stress and inhibition of sarco/ER calcium-ATPase (SERCA) without significant increase in serum alanine aminotransferase (ALT) levels. However, a single dose of alcohol plus the two HIV PIs caused a more than five-fold increase in serum ALT, a synergistic increase in alcohol-induced liver lipid accumulation and ER stress response, and a decrease of SERCA. Mice treated with chronic HIV PIs and alcohol developed moderate liver fibrosis. In PMHs, the HIV drugs plus alcohol also inhibited SERCA expression and increased expression of glucose-regulated protein 78, C/EBP homologous protein, sterol regulatory element-binding protein 1c, and phosphorylated c-Jun N-terminal kinase 2, which were accompanied by a synergistic increase in cell death compared with alcohol or the HIV drugs alone. In PHHs, treatment with RIT and LOP or alcohol alone increased messenger RNA of spliced X box-binding protein 1 and decreased SERCA, which were accompanied by reduced levels of intracellular calcium. Alcohol combined with the HIV drugs significantly reduced intracellular calcium levels and potentiated cell death, which was comparable to the cell death caused by the SERCA inhibitor thapsigargin.

CONCLUSION

Our findings suggest the possibility that HIV PIs potentiate alcohol-induced ER stress and injury through modulation of SERCA and maintaining calcium homeostasis could be a therapeutic aim for better care of HIV patients.

Effect of HIV-1 infection and sex on the cellular pharmacology of the antiretroviral drugs zidovudine and lamivudine

The cellular pharmacology of zidovudine (ZDV) and lamivudine (3TC) in vivo is not completely understood. This prospective longitudinal study investigated the relationship between HIV-1 serostatus, sex, race, and time on therapy with intracellular and plasma ZDV and 3TC concentrations. Of 20 HIV-seronegative and 23 HIV-seropositive volunteers enrolled, 16 (8 women) and 21 (5 women) completed all 12 study days, respectively. Volunteers began ZDV-3TC therapy (plus a third active drug in HIV-seropositive volunteers), and steady-state concentrations (C(ss)) were determined after days 1, 3, 7, and 12. A repeated-measures mixed model was utilized. HIV-seronegative status was associated with 22% (95% confidence interval [CI], 0%, 50%) and 37% (15%, 67%) higher C(ss) estimates compared to those of HIV-seropositive individuals for intracellular ZDV-TP and 3TC-TP levels, respectively. African-Americans had 36% (8%, 72%) higher ZDV-TP estimates than non-African-Americans. Sex was not associated with ZDV-TP or 3TC-TP (P > 0.19). Women had 36% (4%, 78%) higher plasma ZDV, but the effect was lessened when normalized by lean body weight (5% [-19%, 38%]; P = 0.68). Plasma 3TC was 19% (0%, 41%) higher in HIV-seropositive volunteers and 22% (0%, 48%) higher in African American volunteers, but these effects were not significant when corrected for creatinine clearance (7% [-9%, 20%] and -5% [-26%, 12%] for HIV serostatus and race, respectively; P > 0.35). These results suggest that HIV-seropositive status decreases and African American race elevates the cellular triphosphates of ZDV and 3TC. This information extends knowledge of ZDV and 3TC cellular pharmacology in vivo and provides new leads for future cellular pharmacology studies aimed at optimizing HIV prevention/treatment with these agents.

Effects of ritonavir-boosted lopinavir on the pharmacokinetics of quinine

The centuries-old antimalarial drug, quinine, continues to play a critical role in the treatment of severe falciparum malaria and uncomplicated malaria in pregnant women. It shares cytochrome P450 (CYP )-mediated metabolic pathways with several commonly used antiretroviral drugs, raising the potential for clinically important drug–drug interactions. A phase I pharmacokinetic study was conducted to assess the impact of long-term use of ritonavir-boosted lopinavir (LPV/r) on quinine pharmacokinetics in healthy volunteers. LP V/r significantly decreased the exposure of quinine and its major active metabolite, 3-hydroxyquinine, in both total and free (unbound) forms. These findings highlight the complex nature of the influence exerted by LPV/r on several of the drug-metabolizing enzymes involved in quinine disposition,including CYP 3A4, UDP-glucuronosyltransferase (UG T), and P-glycoprotein (P-gp). A decline in quinine exposure may compromise clinical efficacy. Further studies are warranted to assess changes in quinine pharmacokinetics and treatment outcomes in patients with acute malaria receiving antiretroviral therapy that includes LPV/r.

Drug-drug interaction analysis of pyronaridine/artesunate and ritonavir in healthy volunteers

A multiple dose, parallel group study was conducted to assess for a drug-drug interaction between the pyronaridine/artesunate (PA) combination antimalarial and ritonavir. Thirty-four healthy adults were randomized (1:1) to receive PA for 3 days or PA with ritonavir (100 mg twice daily for 17 days, PA administered on Days 8–10). Pharmacokinetic parameters for pyronaridine, artesunate, and its active metabolite dihydroartemisinin (DHA) were obtained after the last PA dose and for ritonavir on Days 1 and 10. Ritonavir coadministration did not markedly change pyronaridine pharmacokinetics but resulted in a 27% increase in artesunate area under the curve (AUC) and a 38% decrease in DHA AUC. Ritonavir exposure was increased 3.2-fold in the presence of PA. The only relevant safety observations were increases in liver enzymes, only reaching a clinically significant grade in the PA + ritonavir arm. It was concluded that coadministered ritonavir and PA interact to alter exposure to artesunate, DHA, and ritonavir itself.

Prescription long-term opioid use in HIV-infected patients

OBJECTIVES

To examine changes the in use of prescription opioids for the management of chronic noncancer pain in human immunodeficiency virus (HIV)-infected patients and to identify patient characteristics associated with long-term use.

METHODS

Long-term prescription opioid use (ie, 120+ days supply or 10+ prescriptions during a year) was assessed between 1997 and 2005 among 6939 HIV-infected Kaiser Permanente members and HIV-uninfected persons in the general health plan memberships.

RESULTS

In 2005, 8% of HIV individuals had prevalent long-term opioid use, more than double the prevalence among HIV-uninfected individuals. However, the large increases in use from 1997 to 2005 in the general population were not observed for HIV-infected individuals. The strongest associations with prevalent use among HIV-infected individuals were female sex with a prevalence ratio (PR) of 1.8 (95% CI=1.3, 2.5); Charlson comorbidity score of 2 or more (compared with a score of 0) with a PR of 1.9 (95% CI=1.4, 2.8); injection drug use history with a PR of 1.8 (95% CI=1.3, 2.6); and substance use disorders with a PR of 1.8 (95% CI=1.3, 2.5). CD4, HIV viral load, and acquired immunodeficiency syndrome diagnoses were associated with prevalent opioid use early in the antiretroviral therapy era (1997), but not in 2005.

CONCLUSIONS

Long-term opioid use for chronic pain has remained stable over time for HIV patients, whereas its use increased in the general population. The prevalence of prescribed opioids in HIV patients was highest for certain subgroups, including women, and those with a comorbidity and substance abuse history.