How much ritonavir is needed to boost protease inhibitors? Systematic review of 17 dose-ranging pharmacokinetic trials

An orally bioavailable SARS-CoV-2 main protease inhibitor exhibits improved affinity and reduced sensitivity to mutations

Inhibitors of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) main protease (Mpro) such as nirmatrelvir (NTV) and ensitrelvir (ETV) have proven effective in reducing the severity of COVID-19, but the presence of resistance-conferring mutations in sequenced viral genomes raises concerns about future drug resistance. Second-generation oral drugs that retain function against these mutants are thus urgently needed. We hypothesized that the covalent hepatitis C virus protease inhibitor boceprevir (BPV) could serve as the basis for orally bioavailable drugs that inhibit SARS-CoV-2 Mpro more efficiently than existing drugs. Performing structure-guided modifications of BPV, we developed a picomolar-affinity inhibitor, ML2006a4, with antiviral activity, oral pharmacokinetics, and therapeutic efficacy similar or superior to those of NTV. A crucial feature of ML2006a4 is a derivatization of the ketoamide reactive group that improves cell permeability and oral bioavailability. Last, ML2006a4 was found to be less sensitive to several mutations that cause resistance to NTV or ETV and occur in the natural SARS-CoV-2 population. Thus, anticipatory design can preemptively address potential resistance mechanisms to expand future treatment options against coronavirus variants.

Class-Based Antiretroviral Exposure and Cognition Among Women Living with HIV

Neurologic complications of the human immunodeficiency virus (HIV) are common in treated individuals, and toxicity of certain antiretroviral therapies (ART) may contribute to cognitive impairment. We investigated exposures to specific ART and cognition among women living with HIV (WLWH). Virologically suppressed (viral load <200 copies/mL during at least two semi-annual visits) WLWH and age/race matched HIV-seronegative controls enrolled in the Women's Interagency HIV Study who completed at least two biennial cognitive assessments were included. Analysis of WLWH was restricted to those with exposure to the drug class of interest and a nucleoside reverse transcriptase inhibitor (NRTI) backbone. Generalized estimating equations were used to evaluate repeated measures of cognition over time in association with ART class exposure. Among 1,242 eligible WLWH, 20% (n = 247) had isolated drug exposure to non-nucleoside reverse transcriptase inhibitors (NNRTI), 18% (n = 219) to protease inhibitors (PIs), and 6% (n = 79) to integrase inhibitors with a NRTI backbone. Cognitive assessments were performed at a median of 3 biennial visits {IQR 2-4 visits}. At the index assessment, 21% of WLWH demonstrated global cognitive impairment versus 29% at their last cognitive assessment. In multivariable analyses adjusted for hypertension, depression, diabetes mellitus, history of AIDS-defining illness, alcohol use, number of medications, and time on ART, WLWH exposed to NNRTIs demonstrated verbal learning improvements (mean T-score change 1.3, p = .020) compared to other treated women. Compared to HIV-seronegative women, WLWH exposed to PIs had worse verbal learning (mean T-score difference -2.62, p = .002) and verbal memory performance (mean T-score difference -1.74, p = .032) at baseline. Compared to HIV-seronegative women, WLWH exposed to PIs had improvements in verbal learning (mean T-score slope difference 0.36, p = .025) and verbal memory (mean T-score slope difference 0.32, p = .042). The index T-score and slope of change in the T-score were similar among other treated groups and the HIV-seronegative group. We noted emerging trends in cognition in WLWH exposed to specific drug classes. Ongoing study of this relatively young group is important to characterize long-term cognitive outcomes and effect of antiretrovirals as treatment guidelines evolve.

Breaking Bad Patents: Learning from HIV/AIDS to make COVID-19 treatments accessible

The COVID-19 pandemic has brought renewed attention to the topic of challenging drug patents in the interest of public health. Pharmaceutical companies have already begun to patent existing medicines for the treatment and prevention of SARS-CoV-2, affording them exclusive manufacturing rights over vital medicines. Advocates have raised concerns regarding the pricing of COVID-19 drugs, as well as patent monopolies on the manufacture of COVID-19 treatments. The HIV/AIDS pandemic provides a useful lens through which we can analyse existing pathways for challenging pharmaceutical patents in the context of global pandemic. In this article, we review three legal pathways for overriding and seizing patents on medicines by describing cases in which they were employed to make antiretroviral drugs more accessible to people living with HIV. Last, we highlight the weaknesses inherent in these pathways and offer advocacy and policy suggestions for how to strengthen these pathways to improve access to COVID-19 treatments as they become available in the United States and globally.

Herb-Drug Interactions: Worlds Intersect with the Patient at the Center

This review examines three bodies of literature related to herb-drug interactions: case reports, clinical studies, evaluations found in six drug interaction checking resources. The aim of the study is to examine the congruity of resources and to assess the degree to which case reports signal for further study. A qualitative review of case reports seeks to determine needs and perspectives of case report authors. Methods: Systematic search of Medline identified clinical studies and case reports of interacting herb-drug combinations. Interacting herb-drug pairs were searched in six drug interaction resources. Case reports were analyzed qualitatively for completeness and to identify underlying themes. Results: Ninety-nine case-report documents detailed 107 cases. Sixty-five clinical studies evaluated 93 mechanisms of interaction relevant to herbs reported in case studies, involving 30 different herbal products; 52.7% of these investigations offered evidence supporting reported reactions. Cohen's kappa found no agreement between any interaction checker and case report corpus. Case reports often lacked full information. Need for further information, attitudes about herbs and herb use, and strategies to reduce risk from interaction were three primary themes in the case report corpus. Conclusions: Reliable herb-drug information is needed, including open and respectful discussion with patients.

CNS Neurotoxicity of Antiretrovirals

The development of novel antiretroviral treatments has led to a significant turning point in the fight against HIV. Although therapy leads to virologic suppression and prolonged life expectancies, HIV-associated neurocognitive disorder (HAND) remains prevalent. While various hypotheses have been proposed to explain this phenomenon, a growing body of literature explores the neurotoxic effects of antiretroviral therapy. Research to date brings into question the potential role of such medications in neurocognitive and neuropsychiatric impairment seen in HIV-positive patients. This review highlights recent findings and controversies in cellular, molecular, and clinical neurotoxicity of antiretrovirals. It explores the pathogenesis of such toxicity and relates it to clinical manifestations in each medication class. The concept of accelerated aging in persons living with HIV (PLWH) as well as potential treatments for HAND are also discussed. Ultimately, this article hopes to educate clinicians and basic scientists about the neurotoxic effects of antiretrovirals and spur future scientific investigation into this important topic. Graphical Abstract.

Recent progress of antiviral therapy for coronavirus disease 2019

The coronavirus disease 2019 (COVID-19) pandemic has become a global public health crisis, for which antiviral treatments are considered mainstream therapeutic approaches. With the development of this pandemic, the number of clinical studies on antiviral therapy, including remdesivir, chloroquine and hydroxychloroquine, lopinavir/ritonavir, ribavirin, arbidol, interferon, favipiravir, oseltamivir, nitazoxanide, nelfinavir, and camostat mesylate, has been increasing. However, the efficacy of these antiviral drugs for COVID-19 remains controversial. In this review, we summarize the recent progress and findings on antiviral therapies, aiming to provide clinical support for the management of COVID-19. In addition, we analyze the causes of controversy in antiviral drug research and discuss the quality of current studies on antiviral treatments. High-quality randomized clinical trials are required to demonstrate the efficacy and safety of antiviral drugs for the treatment of COVID-19.

Assessment of Clinical Drug-Drug Interactions of Elagolix, a Gonadotropin-Releasing Hormone Receptor Antagonist

Elagolix is an oral gonadotropin-releasing hormone receptor antagonist indicated for the management of endometriosis-associated pain and in combination with estradiol/norethindrone acetate indicated for the management of heavy menstrual bleeding associated with uterine leiomyomas (fibroids) in premenopausal women. Elagolix coadministered with estradiol/norethindrone acetate is in late-stage development for the management of heavy menstrual bleeding associated with uterine fibroids. Based on the in vitro profile of elagolix metabolism and disposition, 9 drug-drug interaction (DDI) studies evaluating the victim and perpetrator characteristics of elagolix were conducted in 144 healthy volunteers. As a victim of cytochrome P450 (CYPs) and transporter-mediated DDIs, elagolix area under the curve (AUC) increased by ∼2-fold following coadministration with ketoconazole and by ∼5- and ∼2-fold with single and multiple doses of rifampin, respectively. As a perpetrator, elagolix decreased midazolam AUC (90% confidence interval) by 54% (50%-59%) and increased digoxin AUC by 32% (23%-41%). Elagolix decreased rosuvastatin AUC by 40% (29%-50%). No clinically significant changes in exposure on coadministration with sertraline or fluconazole occurred. A elagolix 150-mg once-daily regimen should be limited to 6 months with strong CYP3A inhibitors and rifampin because of the potential increase in bone mineral density loss, as described in the drug label. A 200-mg twice-daily regimen is recommended for no more than 1 month with strong CYP3A inhibitors and not recommended with rifampin. Elagolix is contraindicated with strong organic anion transporter polypeptide B1 inhibitors (eg, cyclosporine and gemfibrozil). Consider increasing the doses of midazolam and rosuvastatin when coadministered with elagolix, and individualize therapy based on patient response. Clinical monitoring is recommended for P-glycoprotein substrates with a narrow therapeutic window (eg, digoxin). Dose adjustments are not required for sertraline, fluconazole, bupropion (or any CYP2B6 substrate), or elagolix when coadministered.

Drug-Drug Interactions with Antiretroviral Drugs in Pregnant Women Living with HIV: Are They Different from Non-Pregnant Individuals?

Background and Objective

Although the separate effects of drug–drug interactions and pregnancy on antiretroviral drug pharmacokinetics have been widely studied and described, their combined effect is largely unknown. Physiological changes during pregnancy may change the extent or clinical relevance of a drug–drug interaction in a pregnant woman. This review aims to provide a detailed overview of the mechanisms, magnitude, and clinical significance of antiretroviral drug–drug interactions in pregnant women.

Methods

We performed a literature search and selected studies that compared the magnitude of drug–drug interactions with antiretroviral drugs in pregnant vs non-pregnant women.

Results

Forty-eight papers examining drug–drug interactions during pregnancy were selected, of which the majority focused on pharmacokinetic boosting. Other selected studies examined the drug–drug interactions between efavirenz and lumefantrine, efavirenz and tuberculosis drugs, etravirine and tenofovir disoproxil fumarate, atazanavir and tenofovir disoproxil, and mefloquine and nevirapine in pregnant compared to non-pregnant women. The clinical significance of antiretroviral drug–drug interactions changed during pregnancy from a minimal effect to a contra-indication. In almost all cases, the clinical significance of a drug–drug interaction was more relevant in pregnant women, owing to the combined effects of pregnancy-induced physiological changes and drug–drug interactions leading to a lower absolute drug exposure.

Conclusions

Multiple studies show that the clinical relevance of a drug–drug interaction can change during pregnancy. Unfortunately, many potential interactions have not been studied in pregnancy, which may place pregnant women living with human immunodeficiency virus and their newborns at risk.

Mitochondrial dysfunctions in HIV infection and antiviral drug treatment

Introduction: With the introduction of highly active anti-retroviral therapy (HAART), treatment of HIV infection has improved radically, shifting the concept of HIV disease from a highly mortal epidemic to a chronic illness which needs systematic management. However, HAART does not target the integrated proviral DNA. Hence, prolonged use of antiviral drugs is needed for sustaining life. As a consequence, severe side effects emerge. Several parameters involve in causing these adverse effects. Mitochondrial dysfunctions were pointed as common factor among them. It is, therefore, necessary to critically examine mitochondrial dysfunction in order to understand the side effects.Areas covered: There are many events involved in causing drug-induced side-effects; in this review, we only highlight mitochondrial dysfunctions as one of the events. We present up-to-date findings on mitochondrial dysfunction caused by HIV infection and antiviral drug treatment. Both in vivo and in vitro studies on mitochondrial dysfunction like change in morphology, membrane depolarization, mitophagy, mitochondrial DNA depletion, and intrinsic apoptosis have been discussed.Expert opinion: Mitochondrial dysfunction is associated with severe complications that often lead to discontinuation or change in treatment regimen. Prior knowledge of side effects of antiviral drugs would help in better management and future research should focus to avoid mitochondrial targeting of antiviral drugs while maintaining their antiviral properties.

Key Pharmacokinetic Essentials of Fixed-Dosed Combination Products: Case Studies and Perspectives

Fixed-dose combinations are gaining popularity because they provide convenience while enhancing patient compliance. Literature examples suggest that many fixed-dose combinations are being rationalized and investigated for their potential utility in therapy. This article provides an introspection into the pharmacokinetic essentials that need to be considered prior to implementing a fixed-dose combination strategy. While the drug-drug interaction potential is an important question for the two drugs in a fixed-dose combination, the occurrence of a drug-drug interaction in itself is not a negative outcome for the proposed fixed-dose combination. However, the magnitude of a drug-drug interaction may require a re-assessment of the doses of the two drugs in a fixed-dose combination. Several case studies are provided and discussed to provide a broad perspective on the topic along with a representative framework and strategy on the development of fixed-dose combinations using key pharmacokinetic parameters.

Detecting drug communities and predicting comprehensive drug-drug interactions via balance regularized semi-nonnegative matrix factorization

Background

Because drug–drug interactions (DDIs) may cause adverse drug reactions or contribute to complex-disease treatments, it is important to identify DDIs before multiple-drug medications are prescribed. As the alternative of high-cost experimental identifications, computational approaches provide a much cheaper screening for potential DDIs on a large scale manner. Nevertheless, most of them only predict whether or not one drug interacts with another, but neglect their enhancive (positive) and depressive (negative) changes of pharmacological effects. Moreover, these comprehensive DDIs do not occur at random, but exhibit a weakly balanced relationship (a structural property when considering the DDI network), which would help understand how high-order DDIs work.

Results

This work exploits the intrinsically structural relationship to solve two tasks, including drug community detection as well as comprehensive DDI prediction in the cold-start scenario. Accordingly, we first design a balance regularized semi-nonnegative matrix factorization (BRSNMF) to partition the drugs into communities. Then, to predict enhancive and degressive DDIs in the cold-start scenario, we develop a BRSNMF-based predictive approach, which technically leverages drug-binding proteins (DBP) as features to associate new drugs (having no known DDI) with other drugs (having known DDIs). Our experiments demonstrate that BRSNMF can generate the drug communities, which exhibit more reasonable sizes, the property of weak balance as well as pharmacological significances. Moreover, they demonstrate the superiority of DBP features and the inspiring ability of the BRSNMF-based predictive approach on comprehensive DDI prediction with 94% accuracy among top-50 predicted enhancive and 86% accuracy among bottom-50 predicted degressive DDIs.

Conclusions

Owing to the regularization of the weak balance property of the comprehensive DDI network into semi-nonnegative matrix factorization, our proposed BRSNMF is able to not only generate better drug communities but also provide an inspiring comprehensive DDI prediction in the cold-start scenario.

Electronic supplementary material

The online version of this article (10.1186/s13321-019-0352-9) contains supplementary material, which is available to authorized users.

Amenamevir: Studies of Potential CYP3A-Mediated Pharmacokinetic Interactions With Midazolam, Cyclosporine, and Ritonavir in Healthy Volunteers

Amenamevir (formerly ASP2151) is a helicase‐primase inhibitor being developed for the treatment of herpesvirus infection. Amenamevir is both a substrate and inducer of cytochrome P450 (CYP) 3A4. Three studies were done in healthy volunteers to investigate potential CYP3A pharmacokinetic interactions with the following drugs: (1) Midazolam (probe substrate for CYP3A): After 10 days’ pretreatment with amenamevir 400 mg daily, geometric mean maximum concentration of drug in blood plasma (C_max) and area under the plasma drug concentration‐time curve from time zero to infinity (AUC_0‐∞) of midazolam 7.5 mg were about 68% and 51%, respectively, of those after midazolam alone. (2) Cyclosporine (substrate and inhibitor of CYP3A): After 5 days’ pretreatment with cyclosporine 100 mg twice daily, geometric mean C_max of amenamevir after 400‐mg and 1200‐mg single doses was, respectively, about 66% and 69%, and AUC_0‐∞ about 82% and 79%, of those after amenamevir alone. (3) Ritonavir (inhibitor of CYP3A): When given with single doses of ritonavir 600 mg, geometric mean C_max of amenamevir after 400‐mg and 1200‐mg single doses was, respectively, about 1.4 and 1.6 times higher, and geometric mean AUC_0‐∞ about 2.6 and 3.3 times higher, than after amenamevir alone. Amenamevir has the potential to be involved in CYP3A‐mediated pharmacokinetic interactions in clinical practice.

Combinatorial CRISPR-Cas9 and RNA Interference Attack on HIV-1 DNA and RNA Can Lead to Cross-Resistance

Many potent antiviral drugs have been developed against HIV-1, and their combined action is usually successful in achieving durable virus suppression in infected individuals. This success is based on two effects: additive or even synergistic virus inhibition and an increase in the genetic threshold for development of drug resistance. More recently, several genetic approaches have been developed to attack the HIV-1 genome in a gene therapy setting. We set out to test the combinatorial possibilities for a therapy based on the CRISPR-Cas9 and RNA interference (RNAi) mechanisms that attack the viral DNA and RNA, respectively. When two different sites in the HIV-1 genome were targeted, either with dual CRISPR-Cas9 antivirals or with a combination of CRISPR-Cas9 and RNAi antivirals, we observed additive inhibition, much like what was reported for antiviral drugs. However, when the same or overlapping viral sequence was attacked by the antivirals, rapid escape from a CRISPR-Cas9 antiviral, assisted by the error-prone nonhomologous end joining (NHEJ) DNA repair machinery, accelerated the development of cross-resistance to the other CRISPR-Cas9 or RNAi antiviral. Thus, genetic antiviral approaches can be combined, but overlap should be avoided.

Pharmacokinetics and Tolerability of Anti-Hepatitis C Virus Treatment with Ombitasvir, Paritaprevir, Ritonavir, with or Without Dasabuvir, in Subjects with Renal Impairment

BACKGROUND

The direct-acting antiviral agent (DAA) combination of ombitasvir and paritaprevir (administered with ritonavir) with (3D regimen) or without (2D regimen) dasabuvir has shown very high efficacy rates in the treatment of chronic hepatitis C virus (HCV) infection. Renal impairment, a common comorbidity in patients with chronic HCV infection, can influence the pharmacokinetics of antiviral agents and hence their efficacy and safety profiles.

OBJECTIVE

The aim of this study was to evaluate the influence of renal impairment on the pharmacokinetics and tolerability of the 3D and 2D regimens.

METHODS

Overall, 24 subjects, six in each of four renal function groups (normal, mild, moderate, and severe), received a single dose of the 3D and 2D regimens in separate dosing periods. Plasma and urine were analyzed to assess the effect of renal impairment on drug exposure.

RESULTS

DAA exposures changed by up to 21, 37, and 50 % in subjects with mild, moderate, and severe renal impairment, respectively, versus subjects with normal renal function. Ritonavir exposure increased with the degree of renal impairment (maximum 114 %). The half-lives of DAAs and ritonavir in subjects with renal impairment were generally comparable with those in healthy subjects. No safety or tolerability concerns arose in this study.

CONCLUSION

The 3D and 2D regimens do not require dose adjustment for patients with HCV infection and concomitant renal impairment.

The pharmacokinetic interaction between ivacaftor and ritonavir in healthy volunteers

AIMS

The aim of this study was to determine the pharmacokinetic interaction between ivacaftor and ritonavir.

METHODS

A liquid chromatography mass spectrometry (LC-MS) method was developed for the measurement of ivacaftor in plasma. An open-label, sequential, cross-over study was conducted with 12 healthy volunteers. Three pharmacokinetic profiles were assessed for each volunteer: ivacaftor 150 mg alone (study A), ivacaftor 150 mg plus ritonavir 50 mg daily (study B), and ivacaftor 150 mg plus ritonavir 50 mg daily after two weeks of ritonavir 50 mg daily (study C).

RESULTS

Addition of ritonavir 50 mg daily to ivacaftor 150 mg resulted in significant inhibition of the metabolism of ivacaftor. Area under the plasma concentration-time curve from time 0 to infinity (AUC_{0-inf obv} ) increased significantly in both studies B and C compared to study A (GMR [95% CI] 19.71 [13.18-31.33] and 19.77 [14.0-27.93] respectively). Elimination half-life (t_1/2 ) was significantly longer in both studies B and C compared to study A (GMR [95% CI] 11.14 [8.72-13.62] and 9.72 [6.68-12.85] respectively). There was no significant difference in any of the pharmacokinetic parameters between study B and study C.

CONCLUSION

Ritonavir resulted in significant inhibition of the metabolism of ivacaftor. These data suggest that ritonavir may be used to inhibit the metabolism of ivacaftor in patients with cystic fibrosis (CF). Such an approach may increase the effectiveness of ivacaftor in 'poor responders' by maintaining higher plasma concentrations. It also has the potential to significantly reduce the cost of ivacaftor therapy.

Bioavailability enhancement of a BCS IV compound via an amorphous combination product containing ritonavir

Objectives

To evaluate the effect of ritonavir (RTV) co-administration on the bioavailability of an amorphous dispersion of acetyl-11-keto-beta-boswellic acid (AKBA) and to develop a pharmaceutically acceptable AKBA–RTV combination tablet.

Methods

A pharmacokinetic (PK) study in rats was conducted to evaluate the influence of RTV co-administration on the oral bioavailability of an AKBA amorphous dispersion. KinetiSol was utilized to enable production of an improved RTV formulation that facilitated the development of an AKBA–RTV combination tablet. Following in-vitro characterization, the PK performance of the tablets was evaluated in male beagles.

Key findings

Co-administration of RTV increased oral absorption of AKBA by about fourfold over the AKBA dispersion alone and approximately 24-fold over the pure compound. The improved RTV amorphous dispersion exhibited similar purity and neutral-phase dissolution to Norvir. The AKBA–RTV combination tablets yielded a substantial increase in AKBA's bioavailability in dogs.

Conclusions

Oral absorption of AKBA is substantially limited by intestinal CYP3A activity and poor aqueous solubility. Consequently, AKBA's oral bioavailability is maximized by administration from a supersaturating formulation in conjunction with a CYP3A inhibitor. The AKBA–RTV combination tablet presented herein represents a breakthrough in the oral delivery of the compound facilitating future use as a drug therapy for broad spectrum cancer treatment.

Pharmacokinetics and pharmacodynamics of boosted once-daily darunavir

The ability to dose antiretroviral agents once daily simplifies the often complex therapeutic regimens required for the successful treatment of HIV infection. Thus, once-daily dosing can lead to improved patient adherence to medication and, consequently, sustained virological suppression and reduction in the risk of emergence of drug resistance. Several trials have evaluated once-daily darunavir/ritonavir in combination with other antiretrovirals (ARTEMIS and ODIN trials) or as monotherapy (MONET, MONOI and PROTEA trials) in HIV-1-infected adults. Data from ARTEMIS and ODIN demonstrate non-inferiority of once-daily darunavir/ritonavir against a comparator and, together with pharmacokinetic data, have established the suitability of once-daily darunavir/ritonavir for treatment-naive and treatment-experienced patients with no darunavir resistance-associated mutations. The findings of ARTEMIS and ODIN have led to recent updates to treatment guidelines, whereby once-daily darunavir/ritonavir, given with other antiretrovirals, is now a preferred treatment option for antiretroviral-naive adult patients and a simplified treatment option for antiretroviral-experienced adults who have no darunavir resistance-associated mutations. Once-daily dosing with darunavir/ritonavir is an option for treatment-naive and for treatment-experienced paediatric patients with no darunavir resistance-associated mutations based on the findings of the DIONE trial and ARIEL substudy. This article reviews the pharmacokinetics, efficacy, safety and tolerability of once-daily boosted darunavir. The feasibility of darunavir/ritonavir monotherapy as a treatment approach for some patients is also discussed. Finally, data on a fixed-dose combination of 800/150 mg of darunavir/cobicistat once daily are presented, showing comparable darunavir bioavailability to that obtained with 800/100 mg of darunavir/ritonavir once daily.

Antiviral treatment of hepatitis C virus infection and factors affecting efficacy

Hepatitis C virus (HCV) infection is the leading cause of chronic liver-related diseases, including cirrhosis, liver failure, and hepatocellular carcinoma. Currently, no effective vaccine is available for HCV infection. Polyethylene glycol interferon-α (PegIFN-α) in combination with ribavirin (RBV) is the standard of care (SOC) for chronic hepatitis C. However, the efficacy of PegIFN-α and RBV combination therapy is less than 50% for genotype 1 HCV, which is the dominant virus in humans. In addition, IFN and RBV have several severe side effects. Therefore, strategies to improve sustained virological response (SVR) rates have been an important focus for clinical physicians. The serine protease inhibitors telaprevir and boceprevir were approved by the United States Food and Drug Administration in 2011. The addition of HCV protease inhibitors to the SOC has significantly improved the efficacy of treatments for HCV infection. Several direct-acting antiviral drugs currently in late-stage clinical trials, both with and without peg-IFN and RBV, have several advantages over the previous SOC, including higher specificity and efficacy, fewer side effects, and the ability to be administered orally, and might be optimal regimens in the future. Factors affecting the efficacy of anti-HCV treatments based on IFN-α include the HCV genotype, baseline viral load, virological response during treatment, host IL28B gene polymorphisms and hepatic steatosis. However, determining the effect of the above factors on DAA therapy is necessary. In this review, we summarize the development of anti-HCV agents and assess the main factors affecting the efficacy of antiviral treatments.

Reversal of multidrug resistance by the inhibition of ATP-binding cassette pumps employing "Generally Recognized As Safe" (GRAS) nanopharmaceuticals: A review

Pumps of the ATP-binding cassette superfamily (ABCs) regulate the access of drugs to the intracellular space. In this context, the overexpression of ABCs is a well-known mechanism of multidrug resistance (MDR) in cancer and infectious diseases (e.g., viral hepatitis and the human immunodeficiency virus) and is associated with therapeutic failure. Since their discovery, ABCs have emerged as attractive therapeutic targets and the search of compounds that inhibit their genetic expression and/or their functional activity has gained growing interest. Different generations of pharmacological ABC inhibitors have been explored over the last four decades to address resistance in cancer, though clinical results have been somehow disappointing. "Generally Recognized As Safe" (GRAS) is a U.S. Food and Drug Administration designation for substances that are accepted as safe for addition in food. Far from being "inert", some amphiphilic excipients used in the production of pharmaceutical products have been shown to inhibit the activity of ABCs in MDR tumors, emerging as a clinically translatable approach to overcome resistance. The present article initially overviews the classification, structure and function of the different ABCs, with emphasis on those pumps related to drug resistance. Then, the different attempts to capitalize on the activity of GRAS nanopharmaceuticals as ABC inhibitors are discussed.

Impact of physiologically based pharmacokinetic modeling and simulation in drug development

Physiologically based pharmacokinetic modeling and simulation can be used to predict the pharmacokinetics of drugs in human populations and to explore the effects of varying physiologic parameters that result from aging, ethnicity, or disease. In addition, the effects of concomitant medications on drug exposure can be investigated; prediction of the magnitude of drug interactions can impact regulatory communications or internal decision-making regarding the requirement for a clinical drug interaction study. Modeling and simulation can also help to inform the design and timings of clinical drug interaction studies, resulting in more efficient use of limited resources and improved planning in addition to promoting mechanistic understanding of observed drug interactions. These approaches have been used in GlaxoSmithKline from drug discovery to registration and have been applied to 41 drugs from a number of therapeutic areas. This report highlights the variety of questions that can be addressed by prospective or retrospective application of modeling and simulation and the impact this can have on clinical drug development (from candidate selection through clinical development to regulatory submissions).

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.

Concentration effect relationship of CYP3A inhibition by ritonavir in humans

PURPOSE

To investigate the dose and concentration dependency of CYP3A inhibition by ritonavir using the established limited sampling strategy with midazolam for CYP3A activity.

METHODS

An open, fixed-sequence study was carried out in 12 healthy subjects. Single ascending doses of ritonavir (0.1-300 mg) were evaluated for CYP3A inhibition in two cohorts using midazolam as a marker substance.

RESULTS

Ritonavir administered as a single oral dose produced a dose-dependent CYP3A inhibition with an ID50 of 3.4 mg. Using the measured ritonavir concentrations an exposure-inhibition effect curve was established with an IC50 of 600 h pmol/L (AUC2-4). Over the ritonavir dose range studied non-linear exposure of ritonavir was observed.

CONCLUSIONS

Ritonavir shows a dose and concentration effect relationship of CYP3A inhibition. In addition, a proposed auto-inhibition of ritonavir metabolism resulted in a non-linear exposure of ritonavir with sub-proportional concentrations at low doses. A time-dependent CYP3A activity may result when inhibitors of CYP3A with short elimination half-lives are used.

Sofosbuvir and ABT-450: terminator of hepatitis C virus?

Combination therapy with peginterferon (pegIFN)-α and ribavirin (RBV) has been the standard of care (SOC) for chronic hepatitis C. Unfortunately, not all patients can achieve a sustained virologic response (SVR) with this regimen. SVR rates are approximately 80% in patients with hepatitis C virus (HCV) genotype 2, 3, 5 and 6 and 40%-50% in patients with genotype 1 and 4. Therefore, strategies to improve SVR rates have been an important issue for clinical physicians. Several direct acting antiviral agents (DAAs) have significantly higher SVR rates when combined with pegIFN-α and RBV than pegIFN-α and RBV alone. Treatments containing DAAs have several advantages over the previous SOC, including higher specificity and efficacy, shorter treatment durations, fewer side effects, and oral administration. Based on these advantages, treatment with pegIFN-α and RBV plus telaprevir or boceprevir has become the current SOC for patients with genotype 1 HCV infection. However, many patients are either not eligible for therapy or decline treatment due to coexisting relative or absolute contraindications as well as an inability to tolerate the hematological side effects and adverse events caused by the new SOC. These factors have contributed to the advent of pegIFN-α-free regimens. The newest therapeutic regimens containing sofosbuvir and ABT-450 have shown promising results. In this review, we summarize the development of anti-HCV agents and the clinical efficacy of sofosbuvir and ABT-450-based therapies as well as the potential for future HCV studies.

Interaction between HIV protease inhibitors (PIs) and hepatic transporters in sandwich cultured human hepatocytes: implication for PI-based DDIs

Although HIV protease inhibitors (PIs) produce profound metabolic interactions through inactivation/inhibition of CYP3A enzymes, their role as victims of transporter-based drug-drug interactions (DDIs) is less well understood. Therefore, this study investigated if the PIs, nelfinavir (NFV), ritonavir (RTV), lopinavir (LPV) or amprenavir (APV) were transported into sandwich-cultured human hepatocytes (SCHH), and whether OATPs contributed to this transport. The findings showed that, except for (3) H-APV, no significant decrease in the total hepatocyte accumulation of the (3) H-PIs was detected in the presence of the corresponding unlabeled PI, indicating that the uptake of the other PIs was not mediated. Further, hepatocyte biliary efflux studies using (3) H-APV and unlabeled APV confirmed this decrease to be due to inhibition of sinusoidal influx transporter(s) and not the canalicular efflux transporters. Moreover, this sinusoidal transport of APV was not OATP-mediated. The results indicate that the hepatic uptake of NFV, RTV or LPV was primarily mediated by passive diffusion. The hepatic uptake of APV was mediated by an unidentified sinusoidal transporter(s). Therefore, NFV, RTV or LPV will not be victims of DDIs involving inhibition of hepatic influx transporters; however, the disposition of APV may be affected if its sinusoidal transport is inhibited.

Simultaneous population pharmacokinetic modelling of atazanavir and ritonavir in HIV-infected adults and assessment of different dose reduction strategies

OBJECTIVES

The objective of this study was to develop a simultaneous population pharmacokinetic (PK) model to describe atazanavir/ritonavir (ATV/RTV) PK (300/100 mg) and to assess the effect of RTV dose reduction on ATV PK. Simulations of ATV concentration-time profiles were performed at doses of ATV/RTV 300/50 mg, 200/50 mg, and 200/100 mg once daily.

METHODS

A total of 288 ATV and 312 RTV plasma concentrations from 30 patients were included to build a population PK model using the stochastic approximation expectation maximization algorithm implemented in MONOLIX 3.2 software.

RESULTS

A one-compartment model with first-order absorption and lag-time best described the data for both drugs in the final simultaneous model. A maximum-effect model in which RTV inhibited the elimination of ATV was used to describe the relationship between RTV concentrations and ATV clearance (CL/F). An RTV concentration of 0.22 mg/L was associated with 50% maximum inhibition of ATV CL/F. The population prediction of ATV CL/F in the absence of RTV was 16.6 L/h (relative standard error, 7.0%), and the apparent volume of distribution and absorption rate constant were 106 L (relative standard error, 8%) and 0.87 per hour (fixed), respectively. Simulated average ATV trough concentrations at ATV/RTV 300/50 mg, 200/50 mg, and 200/100 mg once daily were 45%, 63%, and 33% lower, respectively, than that of the standard dose.

CONCLUSION

Although simulated median ATV trough concentrations after dose reductions were still more than the ATV minimum effective concentration (2.9-, 1.9-, and 3.6-fold for ATV/RTV 300/50 mg, 200/50 mg, and 200/100 mg, respectively); our modeling predicted a high proportion of individuals with subtherapeutic trough concentrations on the 200/50 mg dose. This suggests that 300/50 mg and 200/100 mg dosing are preferred candidate regimens in future clinical studies.

Effect of adherence as measured by MEMS, ritonavir boosting, and CYP3A5 genotype on atazanavir pharmacokinetics in treatment-naive HIV-infected patients

We investigated population pharmacokinetics and pharmacogenetics of ritonavir-boosted atazanavir (ATV), using drug intake times exactly recorded by the Medication Event Monitoring System. The ANRS 134-COPHAR 3 trial was conducted in 35 HIV-infected treatment-naive patients. ATV (300 mg), ritonavir (100 mg), and tenofovir (300 mg) + emtricitabine (200 mg), in bottles with MEMS caps, were taken once daily for 6 months. Six blood samples were collected at week 4 to measure drug concentrations, and trough levels were measured bimonthly. A model integrating ATV and ritonavir pharmacokinetics and pharmacogenetics used nonlinear mixed effects. Use of exact dosing data halved unexplained variability in ATV clearance. The ritonavir-ATV interaction model suggested that optimal boosting effect is achievable at lower ritonavir exposures. Patients with at least one copy of the CYP3A5*1 allele exhibited 28% higher oral clearance. We provide evidence that variability in ATV pharmacokinetics is defined by adherence, CYP3A5 genotype, and ritonavir exposure.

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.

Pharmacokinetics of darunavir/ritonavir in Asian HIV-1-infected children aged ≥7 years

BACKGROUND

The Asian population, in general, has higher antiretroviral concentrations than those who are not Asian, but there are limited pharmacokinetic data for darunavir/ritonavir in Asian children.

METHODS

Thai children aged ≥7 years and with body weight (BW)≥20 kg who were on darunavir/ritonavir for ≥2 weeks underwent 12-h pharmacokinetics with blood sampling before and at 1, 2, 4, 6, 8, 10 and 12 h post-dosing. Darunavir/ritonavir doses were 375/100 mg twice daily (BW 20 to <30 kg, n=12), 450/100 mg twice daily (BW 30 to <40 kg, n=2) or 600/100 mg twice daily (BW ≥40 kg, n=5). Ritonavir 100 mg soft gel capsules were used instead of solution.

RESULTS

Of the 19 children, 8 were female, median age was 13 years (range 7-16) and median BW was 29.4 kg. The median duration of darunavir/ritonavir treatment was 11 months. The geometric mean values for darunavir were 60.3 h×mg/l for the area under the concentration-time curve at 0-12 h (AUC(0-12)), 8.3 mg/l for the maximum concentration (C(max)) and 3.1 for the concentration prior to the next dose (C(12)) with no differences between dosing groups. All had C(12) above the protein binding adjusted 50% effective concentration (EC(50)) of protease inhibitor-resistant virus (0.55 mg/l). The darunavir pharmacokinetic parameters were similar to those in non-Asian individuals from the DELPHI study, in which 13 of 20 with BW<40 kg used 50 or 60 mg ritonavir boosting.

CONCLUSIONS

Thai children aged ≥7 years who were on standard darunavir dosing with 100 mg ritonavir boosting had adequate and comparable darunavir AUC(0-12), C(max) and C(12) to non-Asian children who mainly used lower doses of ritonavir boosting. A ritonavir boosting dose of 100 mg can be used for children weighing ≥20 kg, particularly when lower dose formulations are unavailable or if intolerant to the solution.

Antiretroviral drug interactions: overview of interactions involving new and investigational agents and the role of therapeutic drug monitoring for management

Antiretrovirals are prone to drug-drug and drug-food interactions that can result in subtherapeutic or supratherapeutic concentrations. Interactions between antiretrovirals and medications for other diseases are common due to shared metabolism through cytochrome P450 (CYP450) and uridine diphosphate glucuronosyltransferase (UGT) enzymes and transport by membrane proteins (e.g., p-glycoprotein, organic anion-transporting polypeptide). The clinical significance of antiretroviral drug interactions is reviewed, with a focus on new and investigational agents. An overview of the mechanistic basis for drug interactions and the effect of individual antiretrovirals on CYP450 and UGT isoforms are provided. Interactions between antiretrovirals and medications for other co-morbidities are summarized. The role of therapeutic drug monitoring in the detection and management of antiretroviral drug interactions is also briefly discussed.

Review article: the aetiology, investigation and management of diarrhoea in the HIV-positive patient

BACKGROUND

Diarrhoea is a common presentation throughout the course of HIV disease.

AIM

To review the literature relating to aetiology, investigation and management of diarrhoea in the HIV-infected adult.

METHODS

The PubMed database was searched using major subject headings 'AIDS' or 'HIV' and 'diarrhoea' or 'intestinal parasite'. The search was limited to adults and to studies with >10 patients.

RESULTS

Diarrhoea affects 40-80% of HIV-infected adults untreated with antiretroviral therapy (ART). First-line investigation is by stool microbiology. Reported yield varies with geography and methodology. Molecular and immunological methods and special stains have improved diagnostic yield. Endoscopy is diagnostic in 30-70% of cases of pathogen-negative diarrhoea and evidence supports flexible sigmoidoscopy as a first line screening procedure (80-95% sensitive for CMV colitis), followed by colonoscopy and terminal ileoscopy. Radiology is useful to assess severity, distribution, complications and to diagnose HIV-related malignancies. Side effects and compliance with ART are important considerations in assessment. There is a good evidence base for many specific therapies, but optimal treatment of cryptosporidiosis is unclear and only limited data support symptomatic treatments.

CONCLUSIONS

The immunological response to HIV infection and Antiretroviral therapy remains incompletely understood. Antiretroviral therapy regimens need to be optimised to suppress HIV while minimising side effects. Effective agents for management of cryptosporidiosis are lacking. There is an urgent need for enhanced regional diagnostic facilities in countries with a high prevalence of HIV. The ongoing roll-out of Antiretroviral therapy in low-resource settings will continue to change the aetiology and management of this problem, necessitating ongoing surveillance and study.

Renal excretion of apricitabine in rats: ex vivo and in vivo studies

Apricitabine (ATC) is a novel nucleoside reverse transcriptase inhibitor undergoing phase 2/3 clinical development for the treatment of HIV infection. In this investigation, the renal handling of ATC was evaluated in the isolated perfused rat kidney (IPK) model with follow-up in vivo studies. IPK experiments were performed to characterize the renal excretion of ATC, to probe mechanisms of ATC excretion using known inhibitors of organic cation (cimetidine) and organic anion (probenecid) transport systems, and to screen for potential drug-drug interactions between ATC and clinically relevant medications (dapsone, metformin, pentamidine, stavudine, tenofovir and ritonavir). ATC demonstrated net tubular secretion in the IPK with a baseline excretion ratio (XR) of 2.1 ± 0.56. ATC XR decreased 3.6-fold in the presence of cimetidine and 2-fold in the presence of probenecid. Among the clinically relevant medications, metformin produced the greatest inhibitory effect on ATC excretion. In vivo studies were conducted in rats to evaluate ATC disposition upon co-administration with compounds that showed a significant effect on ATC clearance in the IPK model. Co-administration of cimetidine and trimethoprim significantly reduced ATC renal clearance, but resulted in only a moderate increase in plasma exposure. Metformin had no apparent effect on ATC clearance in rats. These findings indicate that the IPK model is more sensitive to secretory inhibition as compared to in vivo. The medications screened showed minimal effects on ATC renal excretion in the IPK, and should thus be excluded as potential in vivo interactants. Overall, this study generated important information on renal handling of ATC to support its development and commercialization.

Pharmacokinetics of once-daily darunavir-ritonavir and atazanavir-ritonavir over 72 hours following drug cessation

The object of this study was to investigate the pharmacokinetics of darunavir-ritonavir and atazanavir-ritonavir once-daily dosing over 72 h (h) following drug intake cessation. Volunteers received darunavir-ritonavir at 800 and 100 mg, respectively, once daily for 10 days, followed by a 7-day washout period, and atazanavir-ritonavir at 300 and 100 mg, respectively, once daily for 10 days. Full pharmacokinetic profiles were assessed for each phase for the 72 h following day 10. Pharmacokinetic parameters were determined over 24 h and to the last measurable concentration by noncompartmental methods. Seventeen subjects completed the study. The geometric mean (GM) terminal elimination half-life to 72 h of darunavir was 6.48 h, which was lower than the 0- to 24-h half-life (10.70 h). The terminal elimination half-life of atazanavir was 6.74 h, which was lower than the 0- to 24-h half-life (13.72 h). All subjects but one had darunavir concentrations higher than the target of 550 ng/ml for protease-resistant HIV isolates (equivalent to 10 times the protein-binding-corrected 50% inhibitory concentration [IC(50)] for wild-type virus) at 24 h postdose, and 14 out of 17 had concentrations higher than the target at 30 h postdose (GM of 1,088 and 851 ng/ml). All subjects had atazanavir concentrations above the suggested minimum effective concentration of 150 ng/ml (equivalent to 10 times the protein-binding-corrected IC(50) for wild-type virus) at 24 and 30 h postdose (GM of 693 and 392 ng/ml). Two of 17 and 5 of 17 subjects were above target at 48 h postdose while on darunavir-ritonavir and atazanavir-ritonavir. Ritonavir half-life to 72 h was 6.84 h with darunavir and 6.07 with atazanavir. This study investigated the pharmacokinetic forgiveness of two boosted protease inhibitors. Although the rates of decline of darunavir and atazanavir slightly increased as ritonavir concentrations declined, most individuals had concentrations 6 h after the end of the ideal dosing interval of 24 h which were above the cutoff used to define therapeutic concentrations.

Management of HIV infection in treatment-naive patients: a review of the most current recommendations

PURPOSE

The most current guidelines issued by the Department of Health and Human Services (DHHS) on the management of human immunodeficiency virus (HIV) infection in treatment-naive patients are reviewed.

SUMMARY

Treatment guidelines are updated frequently because of the emergence of data demonstrating the risks and benefits of antiretroviral therapy. The DHHS guidelines strongly recommend initiating therapy in patients with certain conditions regardless of CD4 cell count and in patients with CD4 cell counts of <350 cells/mm(3). Although supporting data are less definitive, treatment is also recommended for patients with CD4 cell counts of 350-500 cells/mm(3). Treatment for patients with CD4 cell counts of >500 cells/mm(3) is controversial. Although cumulative observational data and biological evidence support treatment at higher CD4 cell counts, randomized controlled trial data to support this are not available, and the risk of antiretroviral toxicities, resistance, non-adherence, and cost should be considered in individual patients. The preferred regimens have been consolidated to four options, including a dual-nucleoside reverse transcriptase inhibitor backbone (tenofovir plus emtricitabine) with a nonnucleoside reverse transcriptase inhibitor (efavirenz), a ritonavir-boosted protease inhibitor (atazanavir plus ritonavir or darunavir plus ritonavir), or an integrase strand-transfer inhibitor (raltegravir). Regimens are classified as alternative or acceptable when they have potential safety or efficacy concerns, have higher pill burdens, or require more-frequent administration compared with preferred regimens.

CONCLUSION

The DHHS 2011 guidelines advocate earlier antiretroviral therapy initiation than recommended in recent years, and preferred regimens have been refined to maximize efficacy, safety, and quality of life for treatment-naive HIV-infected patients.

Sequential population pharmacokinetic modeling of lopinavir and ritonavir in healthy volunteers and assessment of different dosing strategies

Nonlinear mixed-effects modeling was applied to explore the relationship between lopinavir and ritonavir concentrations over 72 h following drug cessation and also to assess other lopinavir and ritonavir dosing strategies compared to the standard 400-mg-100-mg twice-daily dose. Data from 16 healthy volunteers were included. Possible covariates influencing lopinavir and ritonavir pharmacokinetics were also assessed. Data were modeled first separately and then together by using individually predicted ritonavir pharmacokinetic parameters in the final lopinavir model. The model was evaluated by means of a visual predictive check and external validation. A maximum-effect model in which ritonavir inhibited the elimination of lopinavir best described the relationship between ritonavir concentrations and lopinavir clearance (CL/F). A ritonavir concentration of 0.06 mg/liter was associated with a 50% maximum inhibition of the lopinavir CL/F. The population prediction of the lopinavir CL/F in the absence of ritonavir was 21.6 liters/h (relative standard error, 14.0%), and the apparent volume of distribution and absorption rate constant were 55.3 liters (relative standard error, 10.2%) and 0.57 h(-1) (relative standard error, 0.39%), respectively. Overall, 92% and 94% of the observed concentrations were encompassed by the 95% prediction intervals for lopinavir and ritonavir, respectively, which is indicative of an adequate model. Predictions of concentrations from an external data set (HIV infected) (n = 12) satisfied predictive performance criteria. Simulated lopinavir exposures at lopinavir-ritonavir doses of 200 mg-150 mg and 200 mg-50 mg twice daily were 38% and 65% lower, respectively, than that of the standard dose. The model allows a better understanding of the interaction between lopinavir and ritonavir and may allow a better prediction of lopinavir concentrations and assessments of different dosing strategies.

Pharmacokinetics of plasma lopinavir/ritonavir following the administration of 400/100 mg, 200/150 mg and 200/50 mg twice daily in HIV-negative volunteers

OBJECTIVES

Data suggest that some licensed antiretroviral doses could be reduced. We assessed the safety, tolerability and pharmacokinetics of lopinavir/ritonavir at doses of 400/100, 200/150 and 200/50 mg twice daily in HIV-negative volunteers (http://clinicaltrials.gov/ct2/show/NCT00985543).

METHODS

Male and female volunteers were administered lopinavir/ritonavir at doses of 400/100 mg (two lopinavir/ritonavir Meltrex 200/50 mg tablets, Regimen 1), 200/150 mg (one Meltrex tablet, one 100 mg ritonavir capsule, Regimen 2) and 200/50 mg (one Meltrex tablet, Regimen 3). Each dose was given twice daily for 7 days sequentially, separated by a 7 day wash-out period. Lopinavir/ritonavir steady-state pharmacokinetics was assessed over 12 h at the end of each phase (days 7, 21 and 35). Pharmacokinetic parameters were compared using the 400/100 mg twice daily dose as reference, by determining geometric mean ratios (GMRs) and 90% confidence intervals.

RESULTS

Twenty-two subjects (eight females) completed the study. Lopinavir AUC(0-12) (ng h/mL), C(max) (ng/mL) and the minimum concentration (C(trough)) (ng/mL) for the 400/100, 200/150 and 200/50 mg twice daily doses, respectively, were as follows: 99,599, 73,603 and 45,146; 11,965, 8939 and 6404; and 5776, 4293 and 1749. Lopinavir pharmacokinetic parameters were significantly lower for Regimens 2 and 3: GMR (90% CI) AUC(0-12), 0.74 (0.65-0.84) and 0.45 (0.40-0.51); C(max), 0.75 (0.66-0.85) and 0.54 (0.40-0.60); and C(trough), 0.74 (0.62-0.89) and 0.30 (0.25-0.36), respectively. All subjects taking the 400/100 and 200/150 mg twice daily doses, and 19 (86%) subjects taking 200/50 mg twice daily had lopinavir concentrations above the suggested minimum effective concentration of 1000 ng/mL.

CONCLUSIONS

These pharmacokinetic data show that therapeutic plasma concentrations of lopinavir can be achieved with 200/150 mg of lopinavir/ritonavir twice daily (one Meltrex tablet and one 100 mg ritonavir capsule twice daily).