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Standard‐of‐care HIV pre‐exposure prophylaxis (PrEP) is highly efficacious, but uptake of and persistence on a daily oral pill is low in many settings. Evaluation of alternate PrEP products will require innovation to avoid the unpractically large sample sizes in noninferiority trials. We propose estimating HIV incidence in people not on PrEP as an external counterfactual to which on‐PrEP incidence in trial subjects can be compared. HIV recent infection testing algorithms (RITAs), such as the limiting antigen avidity assay plus viral load used on specimens from untreated HIV positive people identified during screening, is one possible approach. Its feasibility is partly dependent on the sample size needed to ensure adequate power, which is impacted by RITA performance, the number of recent infections identified, the expected efficacy of the intervention, and other factors. Screening sample sizes to support detection of an 80% reduction in incidence for 3 key populations are more modest, and comparable to the number of participants in recent phase III PrEP trials. Sample sizes would be significantly larger in populations with lower incidence, where the false recency rate is higher or if PrEP efficacy is expected to be lower. Our proposed counterfactual approach appears to be feasible, offers high statistical power, and is nearly contemporaneous with the on‐PrEP population. It will be important to monitor the performance of this approach during new product development for HIV prevention. If successful, it could be a model for preventive HIV vaccines and prevention of other infectious diseases. [ABSTRACT FROM AUTHOR]

Background: Hepatitis C virus (HCV) reinfection after successful treatment may reduce the benefits of cure among people who inject drugs.Objective: To evaluate the rate of HCV reinfection for 3 years after successful treatment among people receiving opioid agonist therapy (OAT).Design: A 3-year, long-term, extension study of persons enrolled in the CO-STAR (Hepatitis C Patients on Opioid Substitution Therapy Antiviral Response) study (ClinicalTrials.gov: NCT02105688).Setting: 55 clinical trial sites in 13 countries.Patients: Aged 18 years and older with chronic HCV infection with genotypes 1, 4, or 6 receiving stable OAT.Intervention: No treatments were administered.Measurements: Serum samples were assessed for HCV reinfection. Urine drug screening was performed.Results: Among 296 participants who received treatment, 286 were evaluable for reinfection and 199 were enrolled in the long-term extension study. The rate of HCV reinfection was 1.7 [95% CI, 0.8 to 3.0] per 100 person-years; 604 person-years of follow-up). A higher rate of reinfection was seen among people with recent injecting drug use (1.9 [95% CI, 0.5 to 4.8] per 100 person-years; 212 person-years). Ongoing drug use and injecting drug use were reported by 59% and 21% of participants, respectively, at the 6-month follow-up visit and remained stable during 3 years of follow-up.Limitations: Participants were required to be 80% adherent to OAT at baseline and may represent a population with higher stability and lower risk for HCV reinfection. Rate of reinfection may be underestimated because all participants did not continue in the long-term extension study; whether participants who discontinued were at higher risk for reinfection is unknown.Conclusion: Reinfection with HCV was low but was highest in the first 24 weeks after treatment completion and among people with ongoing injecting drug use and needle-syringe sharing.Primary Funding Source: Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc. [ABSTRACT FROM AUTHOR]

Recombinant viruses hold promise as vectors for vaccines to prevent infectious diseases with significant global health impacts. One of their major limitations is that preexisting anti-vector neutralizing antibodies can reduce T cell responses to the insert antigens; however, the impact of vector-specific cellular immunity on subsequent insert-specific T cell responses has not been assessed in humans. Here, we have identified and compared adenovirus-specific and HIV-specific T cell responses in subjects participating in two HIV-1 vaccine trials using a vaccine vectored by adenovirus serotype 5 (Ad5). Higher frequencies of pre-immunization adenovirus-specific CD [4.sup.+] T cells were associated with substantially decreased magnitude of HIV-specific CD [4.sup.+] T cell responses and decreased breadth of HIV-specific CD [8.sup.+] T cell responses in vaccine recipients, independent of type-specific preexisting Ad5-specific neutralizing antibody titers. Further, epitopes recognized by adenovirus-specific T cells were commonly conserved across many adenovirus serotypes, suggesting that cross-reactivity of preexisting adenovirus-specific T cells can extend to adenovirus vectors derived from rare serotypes. These findings provide what we believe to be a new understanding of how preexisting viral immunity may impact the efficacy of vaccines under current evaluation for prevention of HIV, tuberculosis, and malaria., Introduction Vaccines offer the most effective and durable interventions for the prevention of infectious diseases. Classic approaches to developing highly efficacious vaccines for major global health threats, including HIV, malaria, [...]

The immunologic basis for the potential enhanced HIV-1 acquisition in adenovirus serotype 5 (Ad5)-seropositive individuals who received the Merck recombinant Ad5 HIV-1 vaccine in the STEP study remains unclear. Here we show that baseline Ad5-specific neutralizing antibodies are not correlated with Ad5-specific T lymphocyte responses and that Ad5-seropositive subjects do not develop higher vector-specific cellular immune responses as compared with Ad5-seronegative subjects after vaccination. These findings challenge the hypothesis that activated Ad5-specific T lymphocytes were the cause of the potential enhanced HIV-1 susceptibility in the STEP study., In the phase 2b STEP efficacy study evaluating the Merck recombinant Ad5 (rAd5) vector-based HIV-1 vaccine, vaccinees with baseline Ad5-specific neutralizing antibodies showed a 2.3-fold higher rate of HIV-1 acquisition [...]

Background and Aim: In China, clinical experience with direct‐acting antiviral treatments for hepatitis C virus (HCV) infection is still emerging. C‐CORAL is a phase 3, multinational, placebo‐controlled, double‐blind trial of elbasvir/grazoprevir (EBR/GZR) in participants with HCV infection from the Asia‐Pacific region and Russia. Here, we report the data from participants enrolled in China. Methods: Treatment‐naive participants with chronic HCV genotype (GT) 1, GT4, or GT6 infection were randomly assigned to receive 50 mg EBR/100 mg GZR for 12 weeks (immediate‐treatment group, ITG) or placebo followed by deferred treatment with EBR/GZR (deferred‐treatment group, DTG). The primary efficacy end‐point was sustained virologic response at 12 weeks after completing treatment (SVR12), and the primary safety end‐point was a comparison of safety between participants receiving EBR/GZR and placebo (NCT02251990; Protocol PN‐5172‐067). Results: A total of 152 participants in China were randomly assigned (ITG, n = 115; DTG, n = 37). SVR12 was achieved in 96.7% (146/151) participants overall and in 97.3% (142/146) of those with GT1b infection. Four participants relapsed (GT1b, n = 3; GT6a, n = 1). Drug‐related AEs were reported in 25 (21.7%) and 9 (24.3%) participants receiving EBR/GZR and placebo, respectively; no drug‐related serious adverse events (AEs) occurred. Two (1.7%) participants receiving EBR/GZR had late hepatic transaminase elevations. Patient‐reported outcomes indicate improved quality of life at follow‐up week 4 in participants receiving EBR/GZR compared to placebo. Conclusion: EBR/GZR administered for 12 weeks represents a highly effective and safe treatment option for Chinese individuals with HCV GT1 infection. [ABSTRACT FROM AUTHOR]

Direct‐acting antiviral treatments for chronic hepatitis C virus (HCV) infection are generally safe; however, understanding the safety profile of each regimen is essential for their continued use. Safety data were pooled from 12 clinical trials of elbasvir/grazoprevir (EBR/GZR) that enrolled adult participants with HCV infection. Pooled analyses are presented for participants receiving EBR/GZR for 12 weeks and those receiving EBR/GZR plus ribavirin (RBV) for 16‐18 weeks. Safety data are also presented for participants with comorbidities receiving EBR/GZR for 12 weeks in individual clinical trials (chronic kidney disease [CKD] stage 4/5, inherited blood disorders [IBLD] or receiving opioid agonist therapy [OAT]). Among 1743 participants receiving EBR/GZR for 12 weeks, 1068 (61.3%) reported ≥1 adverse event (AE) and 491 had AEs (28.2%) considered drug‐related. The most frequent AEs were headache (10.6%), fatigue (8.7%), nasopharyngitis (5.8%), nausea (5.1%) and diarrhoea (5.0%). Serious AEs were reported by 37 participants (2.1%), and 12 (0.7%) discontinued treatment due to an AE. In populations with CKD 4/5 or IBLD or receiving OAT, safety was similar in participants receiving EBR/GZR for 12 weeks and those receiving placebo. Some AEs occurred at higher frequencies in participants receiving RBV compared with those receiving EBR/GZR alone: fatigue (32.7% vs 8.7%); headache (21.6% vs 10.6%); and nausea (15.8% vs 5.1%). Safety was similar in participants with and those without cirrhosis. Grade 3/4 alanine aminotransferase elevations were reported in 0.7% participants. EBR/GZR is a safe treatment option for individuals with HCV genotype (GT) 1 or GT4 infections, even those with challenging comorbidities such as CKD or IBLD and those receiving OAT. [ABSTRACT FROM AUTHOR]

Background: In the United States, the number of new cases of hepatitis C virus infection has risen in recent years, driven largely by transmission among young white adults in their 20s and 30s. Herein, we report an integrated analysis of participants with hepatitis C virus infection aged ≤35 years from 12 phase II/III clinical trials of elbasvir/grazoprevir.Methods: Treatment-naive and -experienced adults with hepatitis C virus genotype 1 or 4 infection received elbasvir (50 mg/day)/grazoprevir (100 mg/day) for 12 weeks without ribavirin. Analyses were stratified according to participant age (≤35 years vs >35 years). The primary endpoint was sustained virologic response (hepatitis C virus RNA < lower limit of quantitation at 12 weeks after completion of therapy).Results: Sustained virologic response was achieved by 98.9% (271/274) of participants aged ≤35 years and by 96.9% (2093/2160) aged >35 years. Three participants aged ≤35 years with genotype 1b infection relapsed. Eight participants with genotype 1a infection and baseline non-structural protein 5 A resistance-associated substitutions achieved sustained virologic response. Similarly, all 85 participants aged ≤35 years with genotype 1a infection and no baseline non-structural protein 5 A resistance-associated substitutions achieved sustained virologic response. Safety was favorable, with the incidence of drug-related adverse events similar in younger and older participants (30.1% vs 30.6%). One participant (0.4%) aged ≤35 years and 15 participants (0.7%) aged >35 years discontinued treatment owing to adverse events.Conclusions: Elbasvir/grazoprevir for 12 weeks was safe and highly effective in participants aged ≤35 years with hepatitis C virus genotype 1 or 4 infection. [ABSTRACT FROM AUTHOR]

Background & Aims: Hepatitis C virus (HCV) genotype (GT) 4 infection is prevalent in sub‐Saharan Africa and the Middle East, particularly in Egypt. This study evaluated the safety and efficacy of elbasvir/grazoprevir administered for 8 and 12 weeks in participants with HCV GT4 infection. Methods: In this partially randomized, open‐label multicentre study conducted in France (NCT03111108; Protocol MK5172‐096), treatment‐naive participants with GT4 infection and F0‐F2 fibrosis were randomized 2:1 to elbasvir (50 mg)/grazoprevir (100 mg) for 8 or 12 weeks. Treatment‐naive participants with F3‐F4 fibrosis and all treatment‐experienced participants (F0‐F4) were assigned to elbasvir/grazoprevir for 12 weeks. The primary endpoint was sustained virologic response (SVR) 12 weeks after the end of therapy. Results: One hundred and seventeen participants were enrolled. Among treatment‐naive participants with F0‐F2 fibrosis, SVR was achieved by 94% (50/53) and 96% (26/27) of those receiving elbasvir/grazoprevir for 8 or 12 weeks, respectively, and four participants relapsed. In the 12‐week arm, 95% (35/37) achieved SVR and two participants relapsed. NS5A resistance‐associated substitutions were present at baseline and virologic failure in five of the participants with relapse. Drug‐related adverse events occurred in 42% (n = 22) and 50% (n = 32) of participants receiving 8 and 12 weeks of treatment, respectively. No participant discontinued treatment owing to an adverse event. Conclusion: These data confirm the efficacy of elbasvir/grazoprevir administered for 12 weeks in treatment‐experienced individuals with HCV GT4 infection and those with advanced fibrosis. Treatment‐naive individuals with mild fibrosis can be treated effectively with an 8‐week regimen. [ABSTRACT FROM AUTHOR]

Purpose: Hepatitis C virus (HCV) infection is a major healthcare concern in Russia, where almost 5 million individuals are viremic. Elbasvir/grazoprevir is a fixed-dose combination therapy for the treatment of HCV genotype 1 and genotype 4 infection. The present analysis aimed to assess the safety and efficacy of elbasvir/grazoprevir in individuals with HCV infection enrolled at Russian study sites in the C-CORAL study. Patients and Methods: C-CORAL (Protocol PN-5172-067; NCT02251990) was a Phase 3, placebo-controlled, double-blind study conducted throughout Asia and Russia. Treatment-naive participants with chronic HCV infection were randomly assigned to receive immediate or deferred treatment with elbasvir 50 mg/grazoprevir 100 mg once daily for 12 weeks. Participants in the immediate-treatment group received elbasvir/grazoprevir for 12 weeks, and those in the deferred-treatment group received placebo for 12 weeks, followed by open-label elbasvir/grazoprevir for 12 weeks. The primary endpoint was sustained virologic response at 12 weeks after completion of therapy (SVR12). Results: One hundred and nineteen Russian participants were randomized (immediate-treatment group, n=88; deferred-treatment group, n=31). Most participants were white (99%) with HCV genotype 1b infection (97%) and mild-to-moderate (F0–F2) fibrosis (70%). SVR12 was achieved by 98.9% participants in the immediate-treatment group and by 100% of those receiving deferred elbasvir/grazoprevir in the deferred-treatment group. One participant relapsed with nonstructural protein 5A (NS5A) L28M and Y93H resistance-associated substitutions at baseline and at time of failure. Drug-related adverse events were reported by 19% of participants receiving elbasvir/grazoprevir in the immediate-treatment group and by 16% of those receiving placebo in the deferred-treatment group. No serious adverse event or deaths occurred, and no participant discontinued treatment owing to an adverse event. Conclusion: Elbasvir/grazoprevir for 12 weeks was highly effective in treatment-naive Russian individuals with HCV genotype 1b infection. [ABSTRACT FROM AUTHOR]

Introduction: Some direct-acting antiviral regimens for hepatitis C virus (HCV) infection pose safety or efficacy concerns if coadministered with drugs containing ethinyl estradiol. The present analysis was conducted to examine the impact of concomitant oral contraceptive pills (OCP) or hormone replacement therapy (HRT) during treatment with elbasvir (EBR)/grazoprevir (GZR) in women with HCV genotype (GT)1 or GT4 infection. Methods: This is a post hoc, integrated retrospective analysis of female participants with HCV GT1 or GT4 infection who received EBR 50 mg/GZR 100 mg once daily for 12 weeks in phase 2/3 clinical trials. The primary end point was sustained virologic response at 12 weeks after therapy completion (SVR12). For this analysis, participants were stratified according to whether they received OCP or HRT during the original treatment study. Results: A total of 1,022 women with HCV GT1 or GT4 infection were included (receiving OCP/HRT, n=81; not receiving OCP/HRT, n=941). Most participants receiving OCP/HRT were treatment-naive (79%), noncirrhotic (91.4%), and aged >35 years (71.6%). SVR12 rates were similar in women receiving OCP/HRT and those not receiving OCP/HRT (95.1% vs 96.3%). SVR12 rates remained high across all subgroups within the population receiving OCP/HRT: SVR12 rates were 94.6%, 100%, and 100% in participants with GT1a, GT1b, and GT4 infection, and all women aged 18–35 years achieved SVR (21/21). Treatment-related adverse events occurred in 40.7% (33/81) and 30.1% (283/941) of women receiving and those not receiving OCP/HRT, respectively. Conclusion: The efficacy and safety of EBR/GZR administered for 12 weeks was similar in women receiving OCP/HRT and those not on OCP/HRT. These data indicate that EBR/GZR can be safely used for the treatment of HCV GT1 or GT4 infection in women receiving concomitant OCP/HRT. [ABSTRACT FROM AUTHOR]

Ruzasvir (MK‐8408, an NS5A inhibitor) and uprifosbuvir (MK‐3682, a nonstructural protein 5B nucleotide inhibitor) are highly potent direct‐acting antiviral agents for the treatment of hepatitis C virus (HCV) infection. A phase III clinical trial evaluating the two‐drug combination of ruzasvir 60 mg plus  uprifosbuvir 450 mg suggested suboptimal efficacy in certain HCV genotypes (C‐BREEZE 1; NCT02759315). The aim of the present study was to evaluate the efficacy and safety of ruzasvir in combination with uprifosbuvir administered at a higher dose than that assessed in the earlier study (C‐BREEZE 2: NCT02956629/Merck protocol PN041). Treatment‐naïve or interferon (with or without ribavirin)‐experienced participants with or without compensated cirrhosis were enrolled. All participants received ruzasvir 180 mg plus uprifosbuvir 450 mg once daily for 12 weeks. The primary objectives were the proportion of participants with HCV RNA <15 lU/mL at 12 weeks after the end of study therapy (SVR12), and safety and tolerability of the study drug. Overall, 282 participants were enrolled. SVR12 (n/N) was 91.3% (42/46) in participants infected with HCV genotype (GT) 1a; GT1b, 96.7% (29/30); GT2, 91.5% (43/47); GT3, 73.8% (45/61); GT4, 98.2% (55/56); GT5, 100.0% (18/18); and GT6, 90.9% (20/22). Adverse events (AEs) were reported by 61.3% of participants; drug‐related AEs were reported by 33.3%. The most frequent (≥5% of participants) drug‐related AEs in all participants were fatigue (7.8%) and headache (7.4%). In conclusion, the two‐drug combination of ruzasvir 180 mg plus uprifosbuvir 450 mg for 12 weeks was highly effective and well tolerated in participants infected with HCV GT1, GT2, GT4, GT5 and GT6, with a lower efficacy in GT3‐infected persons. [ABSTRACT FROM AUTHOR]

Background and Aim: Estimates suggest that in Asia, more than 31 million individuals have hepatitis C virus infection. The present analysis was conducted to assess the efficacy and safety of elbasvir/grazoprevir in Asian participants enrolled in the elbasvir/grazoprevir phase 2/3 clinical trials. Methods: This is an integrated analysis of data from 12 international phase 2/3 clinical trials. Asian participants with chronic hepatitis C virus genotype 1 or 4 infection who received elbasvir 50 mg/grazoprevir 100 mg once daily for 12 weeks or elbasvir/grazoprevir plus ribavirin for 16 weeks were included in this analysis. The primary end point was sustained virologic response at 12 weeks after completion of therapy (SVR12). Results: Seven hundred eighty Asian participants from 15 countries were included in this analysis. SVR12 was achieved by 756/780 (96.9%) of all participants, including 748/772 (96.9%) of those who received elbasvir/grazoprevir for 12 weeks and 8/8 (100%) of those who received elbasvir/grazoprevir plus ribavirin for 16 weeks. In the genotype 1b‐infected population, the SVR12 rate was 691/709 (97.5%), and there was no impact of age, high baseline viral load, or presence of cirrhosis. The most frequently reported adverse events were nasopharyngitis (8.0%), upper respiratory tract infection (5.4%), and diarrhea (5.2%). Twenty participants receiving elbasvir/grazoprevir for 12 weeks reported a total of 25 serious adverse events, and 7 (0.9%) discontinued treatment because of an adverse event. Conclusion: Elbasvir/grazoprevir administered for 12 weeks is an effective and generally well‐tolerated treatment option for Asian individuals with hepatitis C virus genotype 1b infection. [ABSTRACT FROM AUTHOR]

Summary: In clinical trials, the three‐drug regimen of ruzasvir (RZR) 60 mg, uprifosbuvir (UPR) 450 mg and grazoprevir 100 mg, with or without ribavirin, has demonstrated promising efficacy and excellent tolerability across a wide range of hepatitis C virus (HCV)‐infected individuals. The present study assessed the efficacy and safety of the two‐drug combination of RZR 60 mg plus UPR 450 mg administered for 12 weeks in participants with HCV genotype (GT) 1‐6 infection. In this open‐label clinical trial, treatment‐naive or ‐experienced and cirrhotic or noncirrhotic participants with chronic HCV GT1‐6 infection received RZR 60 mg plus UPR 450 mg orally once daily for 12 weeks (NCT02759315/protocol PN035). The primary efficacy endpoint was sustained virologic response at 12 weeks after the end of therapy (SVR12). One hundred and sixty participants were enrolled. SVR12 rates were 96% (52 of 54) in participants with GT1a infection; 100% (15 of 15) in those with GT1b infection; 97% (28 of 29) in those with GT2 infection; 77% (30 of 39) in those with GT3 infection; 90% (18 of 20) in those with GT4 infection; and 67% (2 of 3) in those with GT6 infection. Drug‐related adverse events (AEs) reported by >5% of participants were fatigue (n = 10, 6.3%) and diarrhoea (n = 9, 5.6%). Five participants reported a total of 11 serious AEs, none considered drug‐related. One participant experienced on‐treatment alanine aminotransferase/aspartate aminotransferase elevations that resolved without intervention. Data from the present study indicate that the combination of RZR 60 mg plus UPR 450 mg once daily for 12 weeks was well tolerated overall but was effective only for certain genotypes. [ABSTRACT FROM AUTHOR]

Background and Aim: Although treatment with direct‐acting antivirals has dramatically improved morbidity and mortality attributable to chronic hepatitis C virus infection, universal access to these medicines has been slow in the Asia–Pacific region and Russia. This study evaluated efficacy and safety of elbasvir/grazoprevir in participants with hepatitis C virus infection from Asia–Pacific countries and Russia (C‐CORAL). Methods: C‐CORAL was a phase 3, randomized, placebo‐controlled study (NCT02251990). Treatment‐naive, HIV‐negative, cirrhotic and non‐cirrhotic participants with chronic hepatitis C genotype 1, 4, or 6 infection were randomized to elbasvir 50 mg/grazoprevir 100 mg once daily for 12 weeks (immediate‐treatment group) or placebo followed by deferred treatment with elbasvir/grazoprevir (deferred‐treatment group). The primary efficacy outcome was sustained virologic response at 12 weeks, and the primary safety outcome was a comparison between the immediate‐treatment group and placebo phase of the deferred‐treatment group. Results: A total of 489 participants were randomized (immediate‐treatment group, n = 366; deferred‐treatment group, n = 123). Sustained virologic response at 12 weeks in the combined immediate/deferred‐treatment groups was 94.4% (459/486; 95% confidence interval = 92.4–96.5%). Sustained virologic response at 12 weeks was 98.2% in participants with genotype 1b, 91.9% with genotype 1a, and 66.7% with genotype 6 infection. Similar rates of adverse events and drug‐related adverse events were seen in the immediate‐treatment group versus placebo phase of the deferred‐treatment group (51.0% vs 50.4% and 21.4% vs 21.1%). Conclusions: Elbasvir/grazoprevir for 12 weeks represents an effective and well‐tolerated treatment option for treatment‐naive people with genotype 1 infection from Asia–Pacific countries and Russia. [ABSTRACT FROM AUTHOR]

Objectives: A two-part (Phase 1B/3), sequential, open-label, multicentre study evaluated the pharmacokinetics (PK) and safety of intravenous (iv) posaconazole given as antifungal prophylaxis to neutropenic patients with AML or myelodysplastic syndrome (MDS) or to recipients at risk of invasive fungal disease (IFD) after allogeneic HSCT.Methods: Patients (N = 237) received 300 mg of posaconazole iv twice daily on day 1, followed by 300 mg of posaconazole iv once daily for 4-28 days. After at least 5 days, patients were randomly assigned to receive posaconazole oral suspension, 400 mg twice daily or 200 mg three times daily, to complete a 28 day treatment course. Primary PK parameters were steady-state average concentration over the dosing interval (Cavg) and posaconazole trough levels (Cmin).Results: Mean posaconazole Cmin was 1320 ng/mL (day 6) and 1297 ng/mL (day 8); steady-state Cmin was 1090 ng/mL (day 10). Mean steady-state posaconazole Cavg was 1500 ng/mL (day 10 or 14) and was similar in HSCT recipients (1560 ng/mL) and AML/MDS patients (1470 ng/mL). The most commonly reported treatment-related adverse events were diarrhoea (8%), nausea (5%) and rash (5%). IFD was reported in 3/237 patients (1%; 2 proven, 1 probable).Conclusions: Intravenous posaconazole at 300 mg was well tolerated, resulted in adequate steady-state systemic exposure and was associated with a low incidence of IFD in this population at high risk.Trial Registry and Number: ClinicalTrials.gov, NCT01075984. [ABSTRACT FROM AUTHOR]

Background & Aims MK-5172 is an inhibitor of the hepatitis C virus (HCV) nonstructural protein 3/4A protease; MK-5172 is taken once daily and has a higher potency and barrier to resistance than licensed protease inhibitors. We investigated the efficacy and tolerability of MK-5172 with peginterferon and ribavirin (PR) in treatment-naive patients with chronic HCV genotype 1 infection without cirrhosis. Methods We performed a multicenter, double-blind, randomized, active-controlled, dose-ranging, response-guided therapy study. A total of 332 patients received MK-5172 (100, 200, 400, or 800 mg) once daily for 12 weeks in combination with PR. Patients in the MK-5172 groups received PR for an additional 12 or 36 weeks, based on response at week 4. Patients in the control group (n = 66) received a combination of boceprevir and PR, dosed in accordance with boceprevir's US product circular. Results At 24 weeks after the end of therapy, sustained virologic responses were achieved in 89%, 93%, 91%, and 86% of the patients in the groups given the combination of PR and MK-5172 (100, 200, 400, or 800 mg), respectively, vs 61% of controls. In the MK-5172 group receiving 100 mg, 91% of patients had undetectable levels of HCV RNA at week 4 and qualified for the short duration of therapy. The combination of MK-5172 and PR generally was well tolerated. Transient increases in transaminase levels were noted in the MK-5172 groups given 400 and 800 mg, at higher frequencies than in the MK-5172 groups given 100 or 200 mg, or control groups. Conclusions Once-daily MK-5172 (100 mg) with PR for 24 or 48 weeks was highly effective and well tolerated among treatment-naive patients with HCV genotype 1 infection without cirrhosis. Studies are underway to evaluate interferon-free MK-5172--based regimens. ClinicalTrials.gov number: NCT01353911. [ABSTRACT FROM AUTHOR]