Merck Announces Late-Breaking Data from Three Phase 3 Trials Evaluating Doravirine/Islatravir (DOR/ISL), an Investigational, Once-Daily, Two-Drug Regimen for the Treatment of Adults Living with HIV-1 at CROI 2026
DOR/ISL is the first non-INSTI, two-drug regimen to demonstrate non-inferiority and a similar safety profile at Week 48 to BIC/
DOR/ISL maintained virologic suppression at Week 96 in adults with virologically suppressed HIV-1 who switched from other oral antiretroviral therapies, including BIC/
“We are proud to continue building on our 40-year history of HIV research with the presentation of compelling new data from our HIV pipeline at CROI this year,” said Dr.
The Phase 3, double-blind, clinical trial MK-8591A-053 evaluating DOR/ISL versus bictegravir/emtricitabine/tenofovir alafenamidei [(50 mg/200 mg/25 mg),(BIC/
“These new Phase 3 results are meaningful, showing that an investigational two-drug regimen without an INSTI demonstrated non-inferior efficacy and a comparable safety profile versus BIC/
New 96-week data from the Phase 3 MK-8591A-052 and MK-8591A-051 trials evaluating DOR/ISL vs. BIC/
“As people living with HIV age, managing other health conditions becomes a reality for many, making it especially important to have treatment options that can help meet each person’s unique health needs,” said Dr.
About the Phase 3 data from MK-8591A-053
MK-8591A-053 is an ongoing Phase 3 randomized, active-controlled, double-blind, clinical trial evaluating the efficacy and safety of investigational, once-daily DOR/ISL (100 mg/0.25 mg) versus BIC/
At Week 48, virological efficacy as measured by the percentage of participants with HIV-1 RNA levels < 50 copies/mL, was comparable in participants on DOR/ISL versus BIC/
Drug-related AEs were reported in 14.1% of participants on DOR/ISL and 18.0% on BIC/
About the Phase 3 data from MK-8591A-052
MK-8591A-052 is a Phase 3, randomized, active-controlled, double-blind, clinical trial to evaluate the efficacy and safety of a switch to investigational, once-daily DOR/ISL (100 mg/0.25 mg) in adults with HIV-1 infection that has been virologically suppressed on BIC/
At Week 96, DOR/ISL continued to demonstrate similar efficacy compared to BIC/
The safety profile for DOR/ISL at Week 96 continued to be similar to BIC/
About the Phase 3 data from MK-8591A-051
MK-8591A-051 is a Phase 3, open-label randomized, active-controlled, clinical trial to evaluate the efficacy and safety of a switch to investigational, once-daily DOR/ISL (100 mg/0.25 mg) in adults with HIV-1 infection that has been virologically suppressed using bART. In this trial, 551 adults with HIV-1 RNA <50 copies/mL for three months or more on oral 2- or 3-drug ART, with no history of treatment failure and no known virologic resistance to DOR, were randomized 2:1 and switched to DOR/ISL (n= 366) or continued bART (n=185), stratified by bART regimen. The primary efficacy endpoint, percentage of participants with HIV-1 RNA ≥50 copies/mL at Week 48 (non-inferiority margin 4%), was met, demonstrating DOR/ISL to be non-inferior to bART; 1.4% of participants who received DOR/ISL had a viral load of ≥50 copies/mL at Week 48, compared to 4.9% on bART (treatment difference -3.6%, 95% CI -7.8, -0.8). After Week 48 of the comparative portion of the study, all participants received open-label DOR/ISL through Week 144. Results at Week 48 were recently published in
At Week 96, 1.9% of participants who continued on DOR/ISL for 96 weeks had HIV-1 RNA ≥50 copies/mL and 1.1% of participants who switched from bART to DOR/ISL at Week 48. Additionally, 92.6% of participants who were on DOR/ISL through 96 weeks and 96.6% of participants who switched to DOR/ISL at Week 48 maintained virologic suppression (HIV-1 RNA <50 copies/mL) at Week 96.
At Week 96, there were similar rates of drug-related AEs between those who continued on DOR/ISL (13.7%) for 96 weeks and for those who switched from bART to DOR/ISL at Week 48 (11.3%) and rates of discontinuations due to AEs for those on DOR/ISL for 96 weeks (1.1%) and for those who switched from bART to DOR/ISL at Week 48 (0.6%) were similar. The mean percent change in total lymphocyte and CD4 counts were similar for participants who continued on DOR/ISL and switched from bART to DOR/ISL. No participants discontinued treatment due to decreased CD4+ T-cell count or
About Islatravir (MK-8591) and Merck’s
Islatravir (MK-8591) is Merck’s investigational nucleoside analog that blocks HIV-1 replication by multiple mechanisms including inhibition of reverse transcriptase translocation, resulting in immediate chain termination and induction of structural changes in the viral DNA.
Islatravir is under evaluation in multiple ongoing early and late-stage clinical trials in combination with other antiretrovirals for potential daily and once-weekly treatments for HIV-1, with islatravir serving as the anchor medicine in these two-drug regimens.
Islatravir in combination with Gilead’s lenacapavir is in Phase 3 development as a novel oral once-weekly treatment for HIV-1 [ISLEND-1 (NCT06630286) and ISLEND-2 (NCT06630299)], and islatravir in combination with our company’s investigational non-nucleoside reverse transcriptase inhibitor (NNRTI) ulonivirine (MK-8507) is in Phase 2b development (MK-8591B-060, NCT06891066 and MK-8591B-062, NCT07266831) as an oral once-weekly treatment.
MK-8527 is the company’s investigational, novel, once-monthly, oral candidate for pre-exposure prophylaxis (PrEP) for HIV-1. The Phase 3 EXPrESSIVE-11 (MK-8527-011, NCT07044297) trial is evaluating the safety and efficacy of MK-8527 as PrEP to reduce the risk of sexually acquired HIV-1 infection among people likely to be exposed to HIV-1 in 16 countries. The Phase 3 EXPrESSIVE-10 (MK-8527-010, NCT07071623) trial is evaluating the safety and efficacy of MK-8527 as PrEP to reduce the risk of sexually acquired HIV-1 infection among women and adolescent girls in sub-Saharan Africa. Both trials are now enrolling.
For an overview of Merck’s HIV treatment and prevention clinical development program, please click here.
Indications and usage for PIFELTRO® (doravirine) and DELSTRIGO® (doravirine, lamivudine, and tenofovir disoproxil fumarate) in the
PIFELTRO is indicated in combination with other antiretroviral (ARV) agents for the treatment of HIV-1 infection in adult patients with no prior ARV treatment history or to replace the current ARV regimen in those who are virologically suppressed (HIV-1 RNA less than 50 copies per mL) on a stable ARV regimen with no history of treatment failure and no known substitutions associated with resistance to doravirine.
DELSTRIGO is indicated as a complete regimen for the treatment of HIV-1 infection in adult patients with no prior ARV treatment history or to replace the current ARV regimen in those who are virologically suppressed (HIV-1 RNA less than 50 copies per mL) on a stable ARV regimen with no history of treatment failure and no known substitutions associated with resistance to the individual components of DELSTRIGO.
Selected Safety Information
Warning: Posttreatment Acute Exacerbation of Hepatitis B Virus (HBV) for DELSTRIGO
All patients with HIV-1 should be tested for the presence of HBV before initiating ARV therapy. Severe acute exacerbations of HBV have been reported in people with concomitant HIV-1 and HBV who have discontinued products containing lamivudine or tenofovir disoproxil fumarate (TDF), which are components of DELSTRIGO. Patients coinfected with HIV-1 and HBV who discontinue DELSTRIGO should be monitored with both clinical and laboratory follow-up for at least several months after stopping DELSTRIGO. If appropriate, initiation of anti-HBV therapy may be warranted.
Contraindications
PIFELTRO and DELSTRIGO are contraindicated when coadministered with drugs that are strong cytochrome P450 (CYP)3A enzyme inducers (including the anticonvulsants carbamazepine, oxcarbazepine, phenobarbital, and phenytoin; the androgen receptor inhibitor enzalutamide; the antimycobacterials rifampin and rifapentine; the cytotoxic agent mitotane; and the herbal product St. John’s wort (Hypericum perforatum)), as significant decreases in doravirine plasma concentrations may occur, which may decrease the effectiveness of DELSTRIGO and PIFELTRO.
DELSTRIGO is contraindicated in patients with a previous hypersensitivity reaction to lamivudine.
Warnings and Precautions
Severe Skin Reactions
Severe skin reactions, including Stevens-Johnson syndrome (SJS)/toxic epidermal necrolysis (TEN), have been reported during the postmarketing experience with doravirine-containing regimens. Discontinue PIFELTRO or DELSTRIGO, and other medications known to be associated with severe skin reactions, immediately if a painful rash with mucosal involvement or a progressive severe rash develops. Clinical status should be closely monitored, and appropriate therapy should be initiated.
New or Worsening Renal Impairment
Renal impairment, including cases of acute renal failure and Fanconi syndrome, have been reported with the use of TDF. DELSTRIGO should be avoided with concurrent or recent use of a nephrotoxic agent (e.g., high-dose or multiple NSAIDs). Cases of acute renal failure after initiation of high-dose or multiple NSAIDs have been reported in people living with HIV with risk factors for renal dysfunction who appeared stable on TDF.
Prior to or when initiating DELSTRIGO, and during treatment, assess serum creatinine, estimated creatinine clearance, urine glucose, and urine protein in all patients. In patients with chronic kidney disease, also assess serum phosphorus. Discontinue DELSTRIGO in patients who develop clinically significant decreases in renal function or evidence of Fanconi syndrome. Discontinue DELSTRIGO if estimated creatinine clearance declines below 50 mL/min.
Bone Loss and Mineralization Defects
In clinical trials in adults living with HIV, TDF was associated with slightly greater decreases in bone mineral density (BMD) and increases in biochemical markers of bone metabolism. Serum parathyroid hormone levels and 1,25 Vitamin D levels were also higher. Cases of osteomalacia associated with proximal renal tubulopathy have been reported with the use of TDF. The effects of TDF-associated changes in BMD and biochemical markers on long-term bone health and future fracture risk in adults are unknown.
Immune Reconstitution Syndrome
Immune reconstitution syndrome can occur, including the occurrence of autoimmune disorders with variable time to onset, which may necessitate further evaluation and treatment.
Drug Interactions
Because DELSTRIGO is a complete regimen, coadministration with other antiretroviral medications for the treatment of HIV-1 infection is not recommended.
Coadministration of PIFELTRO with efavirenz, etravirine, or nevirapine is not recommended.
If DELSTRIGO is coadministered with rifabutin, take one tablet of DELSTRIGO once daily, followed by one tablet of doravirine (PIFELTRO) approximately 12 hours after the dose of DELSTRIGO.
If PIFELTRO is coadministered with rifabutin, increase PIFELTRO dosage to one tablet twice daily (approximately 12 hours apart).
Consult the full Prescribing Information prior to and during treatment for more information on potential drug-drug interactions.
Dosage and Administration/Specific Populations
Renal Impairment
Because DELSTRIGO is a fixed-dose combination tablet and the dosage of lamivudine and TDF cannot be adjusted, DELSTRIGO is not recommended in patients with estimated creatinine clearance less than 50 mL/min.
Adverse Reactions
The most common adverse reactions with DELSTRIGO (incidence ≥5%, all intensities) were dizziness (7%), nausea (5%), and abnormal dreams (5%). The most common adverse reactions with PIFELTRO (incidence ≥5%, all intensities) were nausea (7%), dizziness (7%), headache (6%), fatigue (6%), diarrhea (6%), abdominal pain (5%), and abnormal dreams (5%).
By week 96 in DRIVE-FORWARD, 2% of adult participants in the PIFELTRO group and 3% in the darunavir+ritonavir (DRV+r) group had adverse events leading to discontinuation of study medication.
By week 96 in DRIVE-AHEAD, 3% of adult participants in the DELSTRIGO group and 7% in the efavirenz (EFV)/emtricitabine (FTC)/TDF group had adverse events leading to discontinuation of study medication.
In DRIVE-FORWARD, mean changes from baseline at week 48 in LDL-cholesterol (LDL-C) and non-HDL-cholesterol (non-HDL-C) were pre-specified. LDL-C: -4.6 mg/dL in the PIFELTRO group vs 9.5 mg/dL in the DRV+r group. Non-HDL-C: -5.4 mg/dL in the PIFELTRO group vs 13.7 mg/dL in the DRV+r group. The clinical benefits of these findings have not been demonstrated.
In DRIVE-AHEAD, mean changes from baseline at week 48 in LDL-C and non-HDL-C were pre-specified. LDL-C: -2.1 mg/dL in the DELSTRIGO group vs 8.3 mg/dL in the EFV/
In DRIVE-SHIFT, mean changes from baseline at week 24 in LDL-C and non-HDL-C were pre-specified. LDL-C: -16.3 mg/dL in the DELSTRIGO group vs -2.6 mg/dL in the PI + ritonavir group. Non-HDL-C: -24.8 mg/dL in the DELSTRIGO group vs -2.1 mg/dL in the PI + ritonavir group. The clinical benefits of these findings have not been demonstrated.
In DRIVE-AHEAD, neuropsychiatric adverse events were reported in the three pre-specified categories of sleep disorders and disturbances, dizziness, and altered sensorium. Twelve percent of adult participants in the DELSTRIGO group and 26% in the EFV/
The safety of DELSTRIGO in virologically suppressed adults was based on week 48 data from participants in the DRIVE-SHIFT trial. Overall, the safety profile in virologically suppressed adult participants was similar to that in participants with no ARV treatment history.
Serum ALT and AST Elevations: In the DRIVE-SHIFT trial, 22% and 16% of participants in the immediate switch group experienced ALT and AST elevations greater than 1.25 X ULN, respectively, through 48 weeks on DELSTRIGO. For these ALT and AST elevations, no apparent patterns with regard to time to onset relative to switch were observed. One percent of participants had ALT or AST elevations greater than 5 X ULN through 48 weeks on DELSTRIGO. The ALT and AST elevations were generally asymptomatic, and not associated with bilirubin elevations. In comparison, 4% and 4% of participants in the delayed switch group experienced ALT and AST elevations of greater than 1.25 X ULN through 24 weeks on their baseline regimen.
Pregnancy/Breastfeeding
There is a pregnancy exposure registry that monitors pregnancy outcomes in individuals exposed to PIFELTRO or DELSTRIGO during pregnancy. Healthcare providers are encouraged to register patients by calling the Antiretroviral Pregnancy Registry (APR) at 1-800-258-4263.
Inform individuals with HIV-1 infection of the potential risks of breastfeeding, including: (1) HIV-1 transmission (in HIV-1–negative infants), (2) developing viral resistance (in HIV-1–positive infants), and (3) serious adverse reactions in a breastfed infant similar to those seen in adults.
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Forward-Looking Statement of
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Risks and uncertainties include but are not limited to, general industry conditions and competition; general economic factors, including interest rate and currency exchange rate fluctuations; the impact of pharmaceutical industry regulation and health care legislation in
The company undertakes no obligation to publicly update any forward-looking statement, whether as a result of new information, future events or otherwise. Additional factors that could cause results to differ materially from those described in the forward-looking statements can be found in the company’s Annual Report on Form 10-K for the year ended
Please see Prescribing Information for PIFELTRO (doravirine)
at:
https://www.merck.com/product/usa/pi_circulars/p/pifeltro/pifeltro_pi.pdf
and
Patient Information for PIFELTRO at:
https://www.merck.com/product/usa/pi_circulars/p/pifeltro/pifeltro_ppi.pdf
Please see Prescribing Information for DELSTRIGO (doravirine, lamivudine, and tenofovir disoproxil fumarate) at:
https://www.merck.com/product/usa/pi_circulars/d/delstrigo/delstrigo_pi.pdf
and
Patient Information for DELSTRIGO at:
https://www.merck.com/product/usa/pi_circulars/d/delstrigo/delstrigo_ppi.pdf
_______________________
ibictegravir/emtricitabine/tenofovir alafenamide (BIKTARVY) is a registered trademark of Gilead Sciences, Inc.
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