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Remdesivir (RDV, Veklury®) is a once-daily, nucleoside ribonucleic acid polymerase inhibitor of severe acute respiratory syndrome coronavirus 2 replication. Remdesivir has been granted approvals in several countries for use in adults and children hospitalized with severe coronavirus disease 2019 (COVID-19). Inside the cell, remdesivir undergoes metabolic activation to form the intracellular active triphosphate metabolite, GS-443902 (detected in peripheral blood mononuclear cells), and ultimately, the renally eliminated plasma metabolite GS-441524. This review discusses the pre-clinical pharmacology of RDV, clinical pharmacokinetics, pharmacodynamics/concentration-QT analysis, rationale for dose selection for treatment of patients with COVID-19, and drug–drug interaction potential based on available in vitro and clinical data in healthy volunteers. Following single-dose intravenous administration over 2 h of an RDV solution formulation across the dose range of 3–225 mg in healthy participants, RDV and its metabolites (GS-704277and GS-441524) exhibit linear pharmacokinetics. Following multiple doses of RDV 150 mg once daily for 7 or 14 days, major metabolite GS-441524 accumulates approximately 1.9-fold in plasma. Based on pharmacokinetic bridging from animal data and available human data in healthy volunteers, the RDV clinical dose regimen of a 200-mg loading dose on day 1 followed by 100-mg maintenance doses for 4 or 9 days was selected for further evaluation of pharmacokinetics and safety. Results showed high intracellular concentrations of GS-443902 suggestive of efficient conversion from RDV into the triphosphate form, and further supporting this clinical dosing regimen for the treatment of COVID-19. Mathematical drug–drug interaction liability predictions, based on in vitro and phase I data, suggest RDV has low potential for drug–drug interactions, as the impact of inducers or inhibitors on RDV disposition is minimized by the parenteral route of administration and extensive extraction. Using physiologically based pharmacokinetic modeling, RDV is not predicted to be a clinically significant inhibitor of drug-metabolizing enzymes or transporters in patients infected with COVID-19 at therapeutic RDV doses. Supplementary Information The online version contains supplementary material available at 10.1007/s40262-021-00984-5.

Remdesivir (RDV), a single diastereomeric monophosphoramidate prodrug that inhibits viral RNA polymerases, has potent in vitro antiviral activity against severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2). RDV received the US Food and Drug Administration (FDA)'s emergency use authorization in the United States and approval in Japan for treatment of patients with severe coronavirus disease 2019 (COVID-19). This report describes two phase I studies that evaluated the safety and pharmacokinetics (PKs) of single escalating and multiple i.v. doses of RDV (solution or lyophilized formulation) in healthy subjects. Lyophilized formulation was evaluated for potential future use in clinical trials due to its storage stability in resource-limited settings. All adverse events were grade 1 or 2 in severity. Overall, RDV exhibited a linear profile following single-dose i.v. administration over 2 hours of RDV solution formulation across the dose range of 3-225 mg. Both lyophilized and solution formulations provided comparable PK parameters. High intracellular concentrations of the active triphosphate (~ 220-fold to 370-fold higher than the in vitro half-maximal effective concentration against SARS-CoV-2 clinical isolate) were achieved following infusion of 75 mg or 150 mg lyophilized formulation over 30 minutes or 2 hours. Following multiple-doses of RDV 150 mg once daily for 7 or 14 days, RDV exhibited a PK profile similar to single-dose administration. Metabolite GS-441524 accumulated ~ 1.9-fold after daily dosing. Overall, RDV exhibited favorable safety and PK profiles that supported once-daily dosing.

Background HCV-specific DAAs have transformed treatment of chronic HCV, but few studies have evaluated these therapies in children. Methods Patients aged 12–17 years old with chronic GT1 HCV were enrolled into an open-label study to receive 12 weeks of LDV/SOF 90 mg/400 mg once daily, and those with HCV GT2 or GT3 to receive SOF (400 mg once daily) + RBV (15 mg/kg/day) for 12 (GT2) or 24 weeks (GT3), respectively. Primary efficacy endpoint was SVR12. Safety was assessed by adverse events and clinical/laboratory data. Pharmacokinetic (PK) sampling was conducted to confirm the appropriateness of the doses. Results 150 adolescents (100 GT1, 13 GT2 and 37 GT3) were enrolled and treated. The majority were female (56%), white (90%), treatment naive (81%), and vertically infected (80%). The mean age was 15 years (range 12–17). LDV, SOF and GS-331007 (primary metabolite) exposures were within the range of adult exposures observed in the SOF and LDV/SOF phase 2/3 studies. The SVR12 rate was 98% in GT1, 100% in GT2 and 97% in GT3; all 3 patients who were considered not to have achieved SVR12 were lost to follow-up. No adverse event (AE) leading to study drug discontinuation or serious AEs have been reported. Conclusion In adolescents, LDV/SOF for 12 weeks and SOF + RBV for 12 or 24 weeks, resulted in a SVR12 rate of 97–100% with no virologic failures. These regimens were well tolerated, demonstrating their potential as an important treatment option for children with HCV infection.

Severe coronavirus disease 2019 (COVID-19) disease, including multisystem inflammatory syndrome, has been reported in children. This report summarizes development of a remdesivir physiologically-based pharmacokinetic (PBPK) model that accurately describes observed adult remdesivir and metabolites exposure and predicts pediatric remdesivir and metabolites exposure. The adult PBPK model was applied to predict pediatric remdesivir and metabolites steady-state exposures using the Pediatric Population Model in SimCYP and incorporated the relevant physiologic and mechanistic information. Model development was based on adult phase I exposure data in healthy volunteers who were administered a 200-mg loading dose of remdesivir intravenous (IV) over 0.5 hours on Day 1, then 100-mg daily maintenance doses of IV over 0.5 hours starting on Day 2 and continuing through Days 5 or 10. Simulations indicated that use of the adult therapeutic remdesivir dosage regimen (200-mg loading dose on Day 1 then 100-mg daily maintenance dose starting on Day 2) in pediatric patients ≥ 40 kg and a weight-based remdesivir dosage regimen (5-mg/kg loading dose on Day 1 then 2.5-mg/kg daily maintenance dose starting on Day 2) in pediatric patients weighing 2.5 to < 40 kg is predicted to maintain therapeutic exposures of remdesivir and its metabolites. The comprehensive PBPK model described in this report supported remdesivir dosing in planned pediatric clinical studies and dosing in the emergency use authorization and pediatric compassionate use programs that were initiated to support remdesivir as a treatment option during the pandemic.

Remdesivir (RDV) is a phosphoramidate prodrug designed to have activity against a broad spectrum of viruses. Following IV administration, RDV is rapidly distributed into cells and tissues and simultaneously metabolized into GS-441524 and GS-704277 in plasma. LC-MS/MS methods were validated for determination of the 3 analytes in human plasma that involved two key aspects to guarantee their precision, accuracy and robustness. First, instability issues of the analytes were overcome by diluted formic acid (FA) treatment of the plasma samples. Secondly, a separate injection for each analyte was performed with different ESI modes and organic gradients to achieve sensitivity and minimize carryover. Chromatographic separation was achieved on an Acquity UPLC HSS T3 column (2.1 × 50 mm, 1.8 μm) with a run time of 3.4 min. The calibration ranges were 4–4000, 2–2000, and 2–2000 ng/mL, respectively for RDV, GS-441524 and GS-704277. The intraday and interday precision (%CV) across validation runs at 3 QC levels for all 3 analytes was less than 6.6%, and the accuracy was within ±11.5%. The long-term storage stability in FA-treated plasma was established to be 392, 392 and 257 days at −70 °C, respectively for RDV, GS-441524 and GS-704277. The validated method was successfully applied in COVID-19 related clinical studies.

Background Treatment with vesatolimod, an investigational, oral, toll-like receptor 7 (TLR7) agonist, leads to sustained viral remission in some non-human primates when combined with anti-envelope antibodies or therapeutic vaccines. We report results of a Phase Ib study evaluating safety, pharmacokinetics, and pharmacodynamics of vesatolimod in adults living with human immunodeficiency virus (HIV)–1. Methods In this double-blind, multicenter, placebo-controlled trial, participants on antiretroviral therapy with screening plasma HIV-1 RNA levels Results A total of 48 individuals were randomly assigned to vesatolimod (n = 36) or placebo (n = 12). Vesatolimod was generally well tolerated, with no study drug–related serious adverse events or adverse events leading to study drug discontinuation. There were no statistically significant changes from baseline in plasma HIV-1 RNA in the vesatolimod groups, compared to placebo. Vesatolimod plasma exposures increased dose proportionally; consistent responses in cytokines, interferon-stimulated gene expression, and lymphocyte activation were observed with increasing dose levels above 4 mg. Peak elevations 24 hours after receipt of a 6 mg dose were >3.9-fold higher for interferon gamma-induced protein 10 (IP-10), interleukin-1 receptor antagonist (IL-1RA), interferon–inducible T-cell alpha chemoattractant (ITAC) when compared to baseline values. Conclusions Vesatolimod was well tolerated at doses ranging from 1 to 12 mg. Immune stimulation was observed at doses above 4 mg, providing rationale for future combination trials in people living with HIV. Clinical Trials Registration NCT02858401.

Ledipasvir/sofosbuvir (Harvoni®), a fixed-dose combination tablet of an NS5A inhibitor ledipasvir and an NS5B polymerase inhibitor sofosbuvir, is approved for the treatment of chronic hepatitis C virus infection. Ledipasvir/sofosbuvir exhibits a favorable drug-drug interaction profile and can be administered with various medications that may be used by hepatitis C virus-infected patients, including patients with comorbidities, such as co-infection with human immunodeficiency virus or immunosuppression following liver transplantation. Ledipasvir/sofosbuvir is not expected to act as a victim or perpetrator of cytochrome P450- or UDP-glucuronosyltransferase 1A1-mediated drug-drug interactions. With the exception of strong inducers of P-glycoprotein, such as rifampin, ledipasvir/sofosbuvir is not expected to act as a victim of clinically relevant drug-drug interactions. As a perpetrator of pharmacokinetic drug-drug interactions via P-glycoprotein/BCRP, ledipasvir/sofosbuvir should not be used with rosuvastatin and elvitegravir/cobicistat/emtricitabine/tenofovir disoproxil fumarate, whereas its co-administration with amiodarone is not recommended because of a pharmacodynamic interaction. This review summarizes a number of drug interaction studies conducted in support of the clinical development of ledipasvir/sofosbuvir.

BACKGROUND AND AIM Sofosbuvir is a nucleotide analog inhibitor of the hepatitis C virus (HCV) NS5B RNA polymerase with pangenotypic potency. This phase 3b study evaluated the safety and efficacy of sofosbuvir + ribavirin ± peginterferon in Chinese patients infected with HCV genotype 1, 2, 3, or 6. METHODS Patients with genotype 1 or 6 received sofosbuvir + peginterferon/ribavirin for 12 weeks or sofosbuvir + ribavirin for 24 weeks, depending on prior treatment and interferon eligibility. Patients with genotype 2 or 3 received sofosbuvir + ribavirin for 12 or 24 weeks, respectively. The primary endpoint was sustained virologic response at 12 weeks after the end of treatment (SVR12). RESULTS Of 389 patients, 42% had genotype 1, 16% genotype 2, 32% genotype 3, and 9% genotype 6. Half were male, 58% were treatment-naive, and 15% had cirrhosis. SVR12 rates for patients receiving 12 weeks of sofosbuvir + peginterferon/ribavirin were 94% (95% confidence interval [CI], 87-98%) for HCV genotype 1 and 97% (95% CI, 84-100%) for genotype 6. SVR12 rates for those receiving sofosbuvir + ribavirin for 24 weeks were 95% (95% CI, 87-99%) for genotype 1, 100% (95% CI, 40-100%) for genotype 6, and 95% (95% CI, 90-98%) for genotype 3. For genotype 2 patients receiving sofosbuvir + ribavirin for 12 weeks, the SVR12 rate was 92% (95% CI, 83-97%). Twenty patients (5%) relapsed. Ten (3%) experienced serious adverse events. Three (

This study evaluated the effect of supratherapeutic exposure of the anti-HCV drug ledipasvir on the QTc interval in healthy subjects. Sixty healthy volunteers were randomized to receive twice-daily blinded ledipasvir (120 mg) or placebo, administered for 10 days each, or single doses of open-label moxifloxacin (400 mg). Serial plasma samples for ledipasvir concentration analysis were collected after each treatment. Triplicate time-matched electrocardiograms were collected at baseline and after each treatment. Change from baseline in the QTc for ledipasvir or moxifloxacin versus placebo was determined using several correction formulas (primary: QTcF [Fridericia's]; secondary: QTcN [population] and QTcI [individual]). Pharmacokinetics and exposure-QTc relationships were evaluated. Ledipasvir AUC0-24 and Cmax achieved approximately 3.7-fold and 4.2-fold, respectively, above exposures observed following administration of ledipasvir/sofosbuvir (90/400 mg) to HCV-infected patients. There was a lack of effect of supratherapeutic ledipasvir on QTc intervals using all correction methods (upper bound of the 2-sided 90%CIs for the mean difference in time-matched baseline-corrected QTc between ledipasvir versus placebo 5 milliseconds, thereby establishing assay sensitivity. Categorical analyses did not demonstrate clinically relevant effects of ledipasvir on QTc intervals or other electrocardiogram parameters. No relationships between ledipasvir plasma concentration and QTc interval were observed. Ledipasvir does not prolong QTc interval. Based on these results and a previous TQT evaluation for sofosbuvir, the fixed-dose combination regimen of ledipasvir/sofosbuvir is not expected to prolong the QTc interval.

Background Treatment for people living with HIV (PLWH) and end stage renal disease (ESRD) on hemodialysis (HD) has previously required complex dose-adjusted regimens. We evaluated a daily regimen of elvitegravir/cobicistat/emtricitabine/tenofovir alafenamide (E/C/F/TAF) and established this treatment as effective and safe, showing that daily TAF resulted in lower plasma tenofovir exposure than a historical comparison of once weekly tenofovir disoproxil fumarate in patients with ESRD on HD. After week (W) 96, participants transitioned to daily B/F/TAF to assess whether efficacy and safety would be maintained on this STR that is guidelines-recommended for PLWH with eGFR > 30 mL/min. Methods Virologically suppressed adult PLWH with ESRD on chronic HD who completed W96 on E/C/F/TAF enrolled in the B/F/TAF extension for 48 weeks. Efficacy was assessed as the proportion of participants with virologic suppression (HIV RNA < 50 copies/mL). Safety was assessed throughout the study, PK was assessed using sparse sampling at W4, 24 and 48. Results 55 enrolled, 36 completed E/C/F/TAF, 10 entered the B/F/TAF extension. The median age was 55 yrs (range 34-63); median time on HD was 4 yrs (range 2-16). All ten participants on B/F/TAF had HIV-1 RNA < 50 c/mL (95% CI 69%, 100%) at W48. All participants had at least 1 adverse event (AE); most were grade 1 or 2 in severity. One participant had a grade 3 AE and 3 had serious AEs; none were considered related to study drug by the investigator. One participant had AEs attributed to study drug (malaise grade 1 and nausea grade 2), which resolved and did not lead to discontinuation of study drug. There were no clinically relevant changes in fasting lipids. In participants with evaluable data (n=2-5 per timepoint), mean bictegravir trough concentrations were lower compared to PLWH not on HD but remained 4- to 7-fold higher than the established protein-adjusted 95% effective concentration (paEC95) of 162 ng/mL against wild-type virus. Conclusion A once daily regimen of B/F/TAF maintained virologic suppression in PLWH on chronic HD. B/F/TAF was well-tolerated with no discontinuations. B/F/TAF may be an effective, safe and convenient once daily STR and ameliorate the need for dose adjustment in appropriate PLWH who require chronic HD. Disclosures Joseph J. Eron, MD, Gilead Sciences (Consultant, Research Grant or Support)Janssen (Consultant, Research Grant or Support)Merck (Consultant)ViiV Healthcare (Consultant, Research Grant or Support) Aimee Wilkin, MD, MPH, Gilead Sciences Inc. (Grant/Research Support, Scientific Research Study Investigator, Advisor or Review Panel member)GlaxoSmithKline (Grant/Research Support)Janssen (Grant/Research Support, Scientific Research Study Investigator, Advisor or Review Panel member)Pfizer (Grant/Research Support) Moti Ramgopal, MD FACP FIDSA, AbbVie (Speaker’s Bureau)Allergan (Speaker’s Bureau)Gilead Sciences Inc. (Consultant, Scientific Research Study Investigator, Speaker’s Bureau)Janssen (Speaker’s Bureau)Merck (Consultant)Viiv Healthcare (Consultant) Olayemi Osiyemi, M.D, GlaxoSmithKline (Advisor or Review Panel member, Speaker’s Bureau)ViiV Healthcare (Advisor or Review Panel member, Speaker’s Bureau) Jihad Slim, MD, Abbvie (Speaker’s Bureau)Gilead (Speaker’s Bureau)Jansen (Speaker’s Bureau)Merck (Speaker’s Bureau)ViiV (Speaker’s Bureau) David Asmuth, MD, Gilead Sciences Inc. (Scientific Research Study Investigator) Edwin DeJesus, MD, Gilead Sciences (Advisor or Review Panel member) Polina German, PharmD, Gilead Sciences (Employee) Christiana Blair, MS, Gilead Sciences (Employee, Shareholder) Christoph C. Carter, MD, Gilead Sciences Inc. (Employee, Shareholder) Diana M. Brainard, MD, Gilead Sciences (Employee) Sean E. Collins, MD, MS, Gilead Sciences (Employee) Hal Martin, MD, MPH, Gilead Sciences Inc. (Employee, Shareholder)

Background Presatovir significantly reduced nasal viral load, signs, and symptoms of respiratory syncytial virus (RSV) infection in a human challenge study. We evaluated presatovir in hematopoietic-cell transplant (HCT) recipients with RSV lower respiratory tract infection (LRTI). Methods Patients with confirmed RSV in upper and lower respiratory tract and new chest X-ray abnormalities were randomized (1:1), stratified by supplemental oxygen and ribavirin use, to receive oral presatovir 200 mg or placebo every 4 days for 5 doses. The primary endpoint was time-weighted average change in nasal RSV viral load through day 9. Secondary endpoints included supplemental oxygen-free days, incident respiratory failure requiring mechanical ventilation, and all-cause mortality. Results From January 31, 2015, to March 20, 2017, 60 patients from 17 centers were randomized (31 presatovir, 29 placebo); 59 received study treatment (50 allogeneic, 9 autologous HCT). In the efficacy population (29 presatovir, 28 placebo), presatovir treatment did not significantly reduce time-weighted average change in viral load (−1.12 vs −1.09 log10 copies/mL; treatment difference −0.02 log10 copies/mL, 95% confidence interval: −.62, .57; P = .94), median supplemental oxygen-free days (26 vs 28 days, P = .84), incident respiratory failure (10.3 vs 10.7%, P = .98), or all-cause mortality (0 vs 7.1%, P = .19) versus placebo. Adverse events were similar between arms (presatovir 80%, placebo 79%). Resistance-associated substitutions in RSV fusion protein emerged in 6/29 presatovir-treated patients. Conclusions Presatovir treatment was well tolerated in HCT patients with RSV LRTI but did not improve virologic or clinical outcomes versus placebo. Clinical Trials Registration www.clinicaltrials.gov, NCT02254421; EudraCT, #2014-002475-29, Presatovir treatment was safe but did not improve viral or clinical outcomes in hematopoietic-cell transplant recipients with respiratory syncytial virus lower respiratory tract infection. Future studies in this population should incorporate novel methods to evaluate virus-related injury and treatment effects.

Tenofovir disoproxil fumarate (TDF) and tenofovir alafenamide (TAF) are both tenofovir (TFV) prodrugs, with the same active intracellular metabolite, TFV-diphosphate (TFV-DP). TAF delivers TFV-DP to target cells more efficiently and at lower doses than TDF, thereby substantially reducing systemic exposure to TFV, which results in improved bone and renal safety relative to TDF. As such, the method developed for the determination of TFV following TAF administration involved two key differences from determination of TFV following TDF administration. First, human plasma samples (500 μL) immediately upon collection were treated with 20% formic acid (40 μL) (plasma: formic acid ratio of 100:8) to minimize hydrolysis of TAF to TFV, and thereby avoided overestimation of TFV concentrations. Second, various TFV validation tests were conducted in the presence of TAF to mimic the high TAF:TFV ratios in clinical samples collected within ~2 h after dosing. The method for determination of TFV was developed and validated at a US lab and followed FDA and EMA guidelines. To support global clinical studies of TAF, the method was cross-validated (one-way) between the US lab and a China lab and was successfully used for TFV determination in plasma samples from a clinical study that involved healthy Chinese subjects.

Background Hematopoietic-cell transplant (HCT) recipients are at risk for severe respiratory syncytial virus (RSV) infection. We evaluated the RSV fusion inhibitor presatovir in a randomized, double-blind, Phase II trial in HCT recipients with RSV upper respiratory tract infections. Methods Patients were stratified by lymphopenia (, Presatovir treatment was safe but did not improve viral or clinical outcomes in hematopoietic-cell transplant recipients with respiratory syncytial virus upper respiratory tract infections. Exploratory analyses suggest clinical benefit in hematopoietic-cell transplant patients with lymphopenia at presentation.

Ledipasvir/sofosbuvir (Harvoni®), a fixed-dose combination tablet of an NS5A inhibitor ledipasvir and an NS5B polymerase inhibitor sofosbuvir, is approved in the US, European Union, Canada, and other regions for the treatment of chronic hepatitis C virus infection in adults. Following absorption, ledipasvir reaches maximum plasma concentrations (T max) 4–4.5 h post-dose and is eliminated with a terminal half-life (t 1/2) of 47 h. Sofosbuvir undergoes intracellular activation to an active triphosphate GS-461203 (not detected in plasma) and ultimately to GS-331007, a predominant circulating metabolite, which is the primary analyte of interest in clinical pharmacology studies. Sofosbuvir is rapidly absorbed and eliminated from plasma (T max: 0.8–1 h; t 1/2: 0.5 h). The peak plasma concentrations for GS-331007 are achieved between 3.5 and 4 h post-dose; the elimination t 1/2 for GS-331007 is 27 h. Ledipasvir/sofosbuvir exhibits a favorable clinical pharmacology profile; it can be administered once daily without regard to food and does not require dose modification in hepatitis C virus-infected patients with any degree of hepatic impairment or mild to moderate renal impairment. The pharmacokinetic profiles of ledipasvir, sofosbuvir, and GS-331007 (predominant circulating metabolite of sofosbuvir) are not significantly affected by demographic variables; pharmacokinetic/pharmacodynamic analyses reveal no exposure-response relationships for efficacy or safety. The review summarizes the clinical pharmacokinetics, pharmacodynamics, and pharmacokinetic/pharmacodynamic analyses for ledipasvir/sofosbuvir.

Effective treatment for hepatitis C virus (HCV) in patients coinfected with human immunodeficiency virus type 1 (HIV-1) remains an unmet medical need.We conducted a multicenter, single-group, open-label study involving patients coinfected with HIV-1 and genotype 1 or 4 HCV receiving an antiretroviral regimen of tenofovir and emtricitabine with efavirenz, rilpivirine, or raltegravir. All patients received ledipasvir, an NS5A inhibitor, and sofosbuvir, a nucleotide polymerase inhibitor, as a single fixed-dose combination for 12 weeks. The primary end point was a sustained virologic response at 12 weeks after the end of therapy.Of the 335 patients enrolled, 34% were black, 55% had been previously treated for HCV, and 20% had cirrhosis. Overall, 322 patients (96%) had a sustained virologic response at 12 weeks after the end of therapy (95% confidence interval [CI], 93 to 98), including rates of 96% (95% CI, 93 to 98) in patients with HCV genotype 1a, 96% (95% CI, 89 to 99) in those with HCV genotype 1b, and 100% (95% CI, 63 to 100) in those with HCV genotype 4. Rates of sustained virologic response were similar regardless of previous treatment or the presence of cirrhosis. Of the 13 patients who did not have a sustained virologic response, 10 had a relapse after the end of treatment. No patient had confirmed HIV-1 virologic rebound. The most common adverse events were headache (25%), fatigue (21%), and diarrhea (11%). No patient discontinued treatment because of adverse events.Ledipasvir and sofosbuvir for 12 weeks provided high rates of sustained virologic response in patients coinfected with HIV-1 and HCV genotype 1 or 4. (Funded by Gilead Sciences; ION-4 ClinicalTrials.gov number, NCT02073656.).

Respiratory syncytial virus (RSV)-associated respiratory tract infection is a leading cause of hospitalizations in infants for which no effective treatment exists. RSV infection is also an important cause of respiratory disease in adults and immunocompromised patients. Presatovir (GS-5806) is an orally bioavailable antiviral agent that inhibits fusion of RSV with host cell membranes. Here, results from 2 phase 1 studies that evaluated safety, tolerability, and pharmacokinetics of presatovir in healthy adults following administration of single and multiple (7 days) once- or twice-daily ascending doses (first-in-human study) and in the presence or absence of food (food effect study) are described. Presatovir exhibited favorable safety and pharmacokinetic profiles that supported once-daily dosing. Presatovir exposure increased in an approximately dose-proportional manner across the evaluated dose range (single doses 25-300 mg; multiple doses 10-75 mg once daily for 7 days). Administration of presatovir with a high-fat meal did not alter exposure, supporting administration without regard to a meal in further clinical studies. These data were subsequently used to inform presatovir dosing regimens in a phase 2a challenge study of adults experimentally infected with RSV. Collectively, results from phase 1 evaluations and a phase 2a challenge study support further clinical investigation of presatovir for the treatment of RSV infection.

Sofosbuvir is a nucleotide analog inhibitor of the hepatitis C virus (HCV) NS5B RNA polymerase with pangenotypic potency. This phase 3b study evaluated the safety and efficacy of sofosbuvir + ribavirin ± peginterferon in Chinese patients infected with HCV genotype 1, 2, 3, or 6.Patients with genotype 1 or 6 received sofosbuvir + peginterferon/ribavirin for 12 weeks or sofosbuvir + ribavirin for 24 weeks, depending on prior treatment and interferon eligibility. Patients with genotype 2 or 3 received sofosbuvir + ribavirin for 12 or 24 weeks, respectively. The primary endpoint was sustained virologic response at 12 weeks after the end of treatment (SVR12).Of 389 patients, 42% had genotype 1, 16% genotype 2, 32% genotype 3, and 9% genotype 6. Half were male, 58% were treatment-naïve, and 15% had cirrhosis. SVR12 rates for patients receiving 12 weeks of sofosbuvir + peginterferon/ribavirin were 94% (95% confidence interval [CI], 87-98%) for HCV genotype 1 and 97% (95% CI, 84-100%) for genotype 6. SVR12 rates for those receiving sofosbuvir + ribavirin for 24 weeks were 95% (95% CI, 87-99%) for genotype 1, 100% (95% CI, 40-100%) for genotype 6, and 95% (95% CI, 90-98%) for genotype 3. For genotype 2 patients receiving sofosbuvir + ribavirin for 12 weeks, the SVR12 rate was 92% (95% CI, 83-97%). Twenty patients (5%) relapsed. Ten (3%) experienced serious adverse events. Three ( 1%) discontinued treatment because of adverse events, of whom one died because of treatment-unrelated adverse events.Sofosbuvir-based regimens were highly effective and safe in Chinese patients with HCV genotype 1, 2, 3, or 6, suggesting sofosbuvir could serve as the backbone for HCV treatment in China irrespective of genotype.

This study evaluated the potential for a drug-drug interaction between HCV direct-acting antivirals sofosbuvir or ledipasvir and oral hormonal contraceptive (OC) norgestimate/ethinyl estradiol (norgestimate 0.18/0.215/0.25 mg with ethinyl estradiol 25 μg). This was a 112-day, open-label, fixed-sequence pharmacokinetic (PK) study in healthy female subjects that included a lead-in cycle (OC only; N = 21), cycle 1 (OC only; N = 15), cycle 2 (OC + sofosbuvir; N = 15), and cycle 3 (OC + ledipasvir; N = 15). Administration of sofosbuvir with OC did not alter PK of norelgestromin (primary norgestimate metabolite) or ethinyl estradiol. Small increases in norgestrel (secondary norgestimate metabolite) AUC(tau) (19%) and C(tau) (23%) with sofosbuvir were noted. Ledipasvir did not impact PK of norelgestromin or norgestrel but modestly increased ethinyl estradiol C(max) (40%). Sofosbuvir, GS- 331007 (predominant circulating metabolite of SOF), and ledipasvir PK were similar to historical data. Pharmacodynamic markers luteinizing hormone, follicle-stimulating hormone, and progesterone values were generally comparable in all cycles. No loss in contraceptive efficacy is expected upon administration of sofosbuvir or ledipasvir/sofosbuvir with oral contraceptives containing norgestimate and ethinyl estradiol. The use of sofosbuvir or ledipasvir/sofosbuvir FDC with oral contraceptives is permitted.

Preclinical characterization of velpatasvir (VEL; GS-5816), an inhibitor of the hepatitis C virus (HCV) NS5A protein, demonstrated that it has favorable in vitro and in vivo properties, including potent antiviral activity against hepatitis C virus genotype 1 to 6 replicons, good metabolic stability, low systemic clearance, and adequate bioavailability and physicochemical properties, to warrant clinical evaluation. The phase 1 (first-in-human) study evaluated the safety, tolerability, and pharmacokinetics of VEL in healthy human subjects following administration of single and multiple ( n = 7) once-daily ascending doses and of VEL in the presence and absence of food. Following administration of single and multiple doses, VEL was safe and well tolerated when administered at up to 450 mg and when administered with food. The pharmacokinetic behavior of VEL observed in humans was generally in agreement with that seen during preclinical characterization. Following administration of multiple doses, VEL trough concentrations were significantly greater than the protein-adjusted half-maximal (50%) effective concentration of VEL against HCV genotype 1 to 6 replicons at all evaluated doses greater than 5 mg. The pharmacokinetics of VEL were not significantly affected by administration with food. Collectively, the results of this study support the further clinical investigation of VEL administered once daily as part of a regimen with other pangenotypic direct-acting antivirals for the treatment of HCV infection.

No all-oral, direct-acting antiviral regimens have been approved for children with chronic hepatitis C virus (HCV) infection. We conducted a phase 2, multicenter, open-label study to evaluate the efficacy and safety of ledipasvir–sofosbuvir in adolescents with chronic HCV genotype 1 infection. One hundred patients aged 12-17 years received a combination tablet of 90 mg ledipasvir and 400 mg sofosbuvir once daily for 12 weeks. On the tenth day following initiation of dosing, 10 patients underwent an intensive pharmacokinetic evaluation of the concentrations of sofosbuvir, ledipasvir, and the sofosbuvir metabolite GS-331007. The primary efficacy endpoint was the percentage of patients with a sustained virologic response at 12 weeks posttreatment. Median age of patients was 15 years (range 12-17). A majority (80%) were HCV treatment-naive, and 84% were infected through perinatal transmission. One patient had cirrhosis, and 42 did not; in 57 patients the degree of fibrosis was unknown. Overall, 98% (98/100; 95% confidence interval 93%-100%) of patients reached sustained virologic response at 12 weeks. No patient had virologic failure. The 2 patients who did not achieve sustained virologic response at 12 weeks were lost to follow-up either during or after treatment. The three most commonly reported adverse events were headache (27% of patients), diarrhea (14%), and fatigue (13%). No serious adverse events were reported. Area under the concentration-time curve (tau) and maximum concentration values for sofosbuvir, ledipasvir, and GS-331007 were within the predefined pharmacokinetic equivalence boundaries of 50%-200% when compared with adults from phase 2 and 3 studies of ledipasvir and sofosbuvir. Conclusion: Ledipasvir−sofosbuvir was highly effective at treating adolescents with chronic HCV genotype 1 infection; the dose of ledipasvir−sofosbuvir currently used in adults was well tolerated in adolescents and had an appropriate pharmacokinetic profile. (Hepatology 2017;66:371–378).

This study evaluated the effect of cobicistat (COBI) on glomerular filtration rate in subjects with normal renal function (RF) or with mild/moderate renal impairment, by comparing creatinine clearance [estimated glomerular filtration rate (eGFR)] with actual GFR (aGFR) using iohexol, a probe drug excreted by glomerular filtration. COBI is a potent CYP3A inhibitor (pharmacoenhancer) currently in phase 3 testing with elvitegravir, atazanavir, and darunavir.Normal RF subjects received COBI 150 mg QD, ritonavir (RTV) 100 mg QD, or placebo for 7 days; subjects with mild/moderate renal impairment received COBI 150 mg QD. The eGFR and aGFR were measured on days 0, 7, and 14 and within-subject changes calculated relative to day 0. COBI and RTV pharmacokinetics were analyzed on day 7.All 36 subjects in cohort 1 and 17 of 18 subjects in cohort 2 completed all study treatments. Study treatments were well tolerated. Small increases in serum creatinine with corresponding mean decreases in eGFR (∼10 mL/min or mL/min per 1.73 m) were observed on day 7 relative to day 0 in subjects receiving COBI (P0.05). The decreases were reversible on COBI discontinuation; mean eGFR values returned to baseline on day 14 (P0.05). No statistically significant changes in aGFR on days 7 or 14 relative to day 0 were seen with COBI (P0.05). No statistically significant decreases in aGFR or eGFR were observed with RTV or placebo.COBI affects eGFR but not the actual GFR. The time to onset, magnitude, and time to resolution of changes in eGFR are consistent with altered proximal tubular secretion of creatinine through inhibition of drug transporters.

Elvitegravir is a potent, boosted, once-daily, HIV integrase inhibitor with antiviral activity against wild-type and drug-resistant strains of HIV. Because elvitegravir is metabolized primarily by cytochrome P450 (CYP) 3A enzymes, coadministration with a strong CYP3A inhibitor such as ritonavir or cobicistat (also known as GS-9350), an investigational pharmacoenhancer, substantially increases (boosts) elvitegravir plasma exposures and prolongs its elimination half-life to ∼9.5 hours, allowing once-daily administration of a low 150 mg dose. Boosting also results in low intra- and intersubject pharmacokinetic variability and high elvitegravir trough concentrations (∼6- to 10-fold above the concentration producing 95% inhibition of wild-type HIV-1 virus [IC95] of 45 ng/mL [protein binding-adjusted]), which is the pharmacokinetic parameter best associated with its antiviral activity. Data from extensive evaluation of the potential for boosted elvitegravir to undergo drug-drug interactions with other antiretroviral agents or concomitant medications indicate the absence of clinically relevant interactions or the need for dose modification in several cases, except for dose reduction of elvitegravir from 150 to 85 mg when coadministered with atazanavir/ritonavir or lopinavir/ritonavir. Dose adjustments for maraviroc and rifabutin, when each is coadministered with boosted elvitegravir, are consistent with their observed interactions with other ritonavir-boosted agents. The presence of a strong CYP3A inhibitor such as ritonavir or cobicistat renders the potential for increase in systemic exposures of CYP3A substrates coadministered with boosted elvitegravir. This article reviews a comprehensive pharmacology programme, including drug-drug interaction studies, mechanistic and special population studies, that has allowed a thorough understanding of elvitegravir clinical pharmacokinetics and its impact on pharmacodynamics.

Objective: This study evaluated the relative bioavailability and pharmacokinetics of elvitegravir (EVG), emtricitabine (FTC), tenofovir disoproxil fumarate (TDF), and a investigational pharmacoenhancer, cobicistat (GS-9350, COBI) coformulated as a fixed-dose combination tablet (FDC) compared with ritonavir-boosted EVG and FTC + TDF in healthy subjects. Methods: Subjects were randomized to 1 of 2 sequences. All treatments were administered in the morning for 10 days with food, separated by a 2-day washout. Blood samples were collected over 24 hours with the last dose of each treatment. Results: Forty-four subjects enrolled, 42 subjects completed all periods. All study treatments were generally well tolerated. Relative to ritonavir-boosted EVG, the geometric least-squares means ratios (GMR) [90% confidence interval (CI)] for EVG area under plasma concentration-time curve from time zero until the end of the dosing interval (AVC) tau , maximum concentration (C max ), and trough concentration (C tau ) were 118 (110 to 126), 108 (100 to 116), and 110 (95.3 to 127), respectively, with EVG/COBI 150 mg/FTC/TDE Relative to FTC + TDF, FTC GMR, and 90% CI were 127 (115 to 140) for AUC tau , 121 (107 to 137) for C max , and 126 (118 to 136) for C tau ; tenofovir (TFV) GMR and 90% CI were 118 (114 to 122), 130 (122 to 138), and 124 (119 to 129) for AUC tau , C max , and C tau respectively, with EVG/COBI 150 mg/FTC/TDF. Conclusions: Fixed-dose combination tablet containing COBI 150 mg resulted in desired high EVG C tau concentrations and clinically equivalent tenofovir and FTC exposures relative to currently approved individual agents and was thus selected for subsequent evaluation.

Malaria, a disease transmitted by the female Anopheles mosquito, has had devastating effects on human populations for more than 4000 years. Treatment of the disease with single drugs, such as chloroquine, sulfadoxine/pyrimethamine or mefloquine, has led to the emergence of resistant Plasmodium falciparum parasites that lead to the most severe form of the illness. Artemisinin-based combination therapies are currently recommended by WHO for the treatment of uncomplicated P. falciparum malaria. Artemisinin and semisynthetic derivatives, including artesunate, artemether and dihydroartemisinin, are short-acting antimalarial agents that kill parasites more rapidly than conventional antimalarials, and are active against both the sexual and asexual stages of the parasite cycle. Artemisinin fever clearance time is shortened to 32 hours as compared with 2-3 days with older agents. To delay or prevent emergence of resistance, artemisinins are combined with one of several longer-acting drugs--amodiaquine, mefloquine, sulfadoxine/pyrimethamine or lumefantrine--which permit elimination of the residual malarial parasites. The clinical pharmacology of artemisinin-based combination therapies is highly complex. The short-acting artemisinins and their long-acting counterparts are metabolized and/or inhibit/induce cytochrome P450 enzymes, and may thus participate in drug-drug interactions with multiple drugs on the market. Alterations in antimalarial drug plasma concentrations may lead to either suboptimal efficacy or drug toxicity and may compromise treatment.

Velpatasvir (VEL; GS-5816) is a potent, pangenotypic hepatitis C virus (HCV), non-structural protein 5A inhibitor in clinical development for the treatment of chronic HCV infection. In vitro studies indicate that VEL may inhibit several drug transporters and be a substrate for enzyme/drug transport systems in vivo. The purpose of this study was to evaluate the potential of VEL as a perpetrator or victim of metabolic- and transporter-based drug–drug interactions using complementary probe drugs. This Phase 1 study was a randomized, cross-over, open-label, single- and multiple-dose, five-cohort study. Serial blood samples were collected following oral administration of reference and test treatments. The primary pharmacokinetic parameters of each analyte were compared when administered alone or in combination. The 90 % confidence intervals (CI) for the ratio of the geometric least-squares means of the test and reference treatments was calculated for each analyte and parameter of interest. This study demonstrated that VEL is a weak (P-gp, OATP) to moderate (breast cancer resistance protein) transport inhibitor. As a victim of interactions, VEL is moderately affected by potent inhibitors and to a greater extent, potent inducers of enzyme/drug transporter systems. The impact of specific transporters and overall contribution of drug transport vs. metabolizing enzymes on the disposition of VEL was characterized through the use of complementary probes, despite the lack of phenotypic specificity, and informs a broad range of drug–drug interaction recommendations.

The World Health Organization recommends the use of artemisinin-based combination therapies (ACTs) for the treatment of uncomplicated malaria. The two most widely adopted ACT regimens are artemether (AR)-lumefantrine (LR) (the combination is abbreviated AL) and amodiaquine (AQ)-artesunate (AS). Pharmacokinetic (PK) data informing the optimum dosing of these drug regimens is limited, especially in children. We evaluated PK parameters in Ugandan children aged 5 to 13 years with uncomplicated malaria treated with AL ( n = 20) or AQ-AS ( n = 21), with intensive venous sampling occurring at 0, 2, 4, 8, 24, and 120 h following administration of the last dose of 3-day regimens of AL (twice daily) or AQ-AS (once daily). AS achieved an estimated maximum concentration in plasma ( C max ) of 51 ng/ml and an area under the concentration-time curve from time zero to infinity (AUC 0-∞ ) of 113 ng·h/ml; and its active metabolite, dihydroartemisinin (DHA), achieved a geometric mean C max of 473 ng/ml and an AUC 0-∞ of 1,404 ng·h/ml. AR-DHA exhibited a C max of 34/119 ng/ml and an AUC 0-∞ of 168/382 ng·h/ml, respectively. For LR, C max and AUC 0-∞ were 6,757 ng/ml and 210 μg·h/ml, respectively. For AQ and its active metabolite, desethylamodiaquine (DEAQ), the C max s were 5.2 ng/ml and 235 ng/ml, respectively, and the AUC 0-∞ s were 39.3 ng·h/ml and 148 μg·h/ml, respectively. Comparison of the findings of the present study to previously published data for adults suggests that the level of exposure to LR is lower in children than in adults and that the level of AQ-DEAQ exposure is similar in children and adults. For the artemisinin derivatives, differences between children and adults were variable and drug specific. The PK results generated for children must be considered to optimize the dosing strategies for these widely utilized ACT regimens.

GS-9350 is a new chemical entity under development as a potent, mechanism-based inhibitor of human cytochrome P450 3A (CYP3A) isoforms. Its intended use is to increase the systemic exposure of coadministered agents that are metabolized by CYP3A enzymes. Unlike ritonavir, which is in current clinical use for this purpose, GS-9350 is devoid of anti-HIV activity. The pharmacokinetics of GS-9350 and its efficacy in increasing systemic exposure of the probe CYP3A substrate midazolam were examined in a study involving single- and multiple-dose escalations of GS-9350 from 50 to 400 mg. Single-dose escalation from 50 to 400 mg resulted in a 164-fold increase in GS-9350 exposure, whereas multiple-dose escalation in the dosage range of 50–300 mg resulted in a 47-fold increase in exposure. GS-9350 potently inhibited midazolam apparent clearance (95% reduction), similar in effect to ritonavir 100 mg. GS-9350 was generally well tolerated at all doses, and there was no evidence of dose-limiting toxicity. Establishing proof-of-concept, GS-9350 is currently under phase II development as a potential alternative to ritonavir for use with antiretroviral agents (including the HIV integrase inhibitor elvitegravir) that are often prescribed along with a “booster” drug. Clinical Pharmacology & Therapeutics (2010) 87 3, 322–329. doi:10.1038/clpt.2009.228

Objectives: Antimalarial combination therapy is used in persons with HIV infection in the absence of data on drug interactions. The objective of this study was to investigate the pharmacokinetics (PK) of antimalarial combination artemether/lumefantrine (AL) when administered with the protease inhibitor combination lopinavir/ ritonavir (LPV/r) in HIV-uninfected healthy volunteers to determine if important drug interactions exist between these agents. Design: Open-label study in healthy HIV-seronegative adults. Methods: Participants received standard 6-dose treatment courses ofAL 80/480 mg twice daily on days 1―4 and 28―31. LPV/r 400/100 mg twice daily was administered on days 16―41 after a 2-week washout period. Plasma concentrations of AL, dihydroartemisinin (DHA, artemether metabolite), lopinavir, and ritonavir were measured. Results: PK of lumefantrine was influenced by LPV/r resulting in 2- to 3-fold increases in area under the curve (AUC) (AUC 0―264 : 413 versus 931 h·μg·mL ―1 ; AUC 0-inf : 456 versus 1073 h·μg·mL ―1 ). For artemether, trends toward C max and AUC decreases (C max 14.3 versus 11.2 ng/mL and 42.7―62.0 versus 25.9―40.5 h·ng·mL ―1 for AUC) were noted during coadministration. For DHA, decreases in C max (58.8 versus 37.3 ng/mL) and AUC (190―198 versus 104―109 h·ng·mL ―1 ) were observed during coadministration without changes in DHA:artemether AUC ratios. AL did not affect LPV/r PK. Conclusions: Coadministration of artmether/lumefantrine and LPV/r can be carried out for patients coinfected with malaria and HIV Formal safety analysis of concomitant therapy should be addressed by future studies among individuals living in malaria-endemic regions.