Merck (MSD ) has announced plans to suspend the dosing of subjects in the Phase II IMAGINE-DR clinical trial of MK-8507 in combination with islatravir (ISL) to treat HIV-1 infection.

The ongoing, randomised, double-blind, controlled, dose-ranging trial is analysing MK-8507 plus ISL, a weekly oral theory, in 161 adult HIV-1 patients.

These subjects were virologically suppressed for over or nearly six months on a once-daily dose of bictegravir/emtricitabine/tenofovir alafenamide (BIC/FTC/TAF).

MK-8507 is an inhibitor of non-nucleoside reverse transcriptase while ISL is a nucleoside reverse transcriptase translocation inhibitor.

The company found a reduction in total lymphocyte and CD4+ T-cell counts in trial subjects who received the combination treatment.

The external Data Monitoring Committee (EDMC ) found that the decreased levels were linked to treatment with ISL plus MK-8507.

Furthermore, steep declines were reported in groups treated with the highest dosages of MK-8507.

Based on advice from the eDMC, Merck decided to stop subject dosing in the trial and will now monitor them.

The company has informed the investigators and paused MK-8507 development.

Merck Research Laboratories Global Clinical Development infectious diseases vice-president Dr Joan Butterton said: “Merck remains resolute in its commitment to help address the unmet needs of people living with HIV and continue to do our part in the global efforts to help end the HIV pandemic, which includes the ongoing development of islatravir.

“All clinical studies provide important learnings to help us in the fight against HIV, and we are grateful to the patients and investigators for their contributions.”

Last week, Merck launched the Phase III VICTOR trial of Verquvo (vericiguat) in people with chronic heart failure who have reduced ejection fraction by 40% or less.

Recruitment of participants who have not experienced a recent worsening heart failure event is underway.