Merck halts development of MK-8507 after release of mid-stage study data

Dosing and development of the MK-8507 drug has been paused with further review of islatravir studies.



Months after talking up it’s significance, the American pharmaceutical Merck & Co have decided to halt the development of MK-8507. The news comes as a setback as the company had initially stated that MK-8507 was a “very important” part of their HIV strategy. The halt was in response to mid-phase data release that indicated that the combination therapy of MK-8507 and islatravir resulted in a decrease of white blood cells in HIV patients. An external data monitoring committee determined that the effect was linked to the once-weekly combination therapy, the biggest dip being with the total lymphocyte and CD4+ T-cell counts in participants who had the highest dose of MK-8507. After recommendation from the committee Merck stopped dosing and will continue to monitor the participants.


The pharmaceutical company “remains confident in islatravir’s overall profile” and will continue to develop the drug, which is an integral part of their internal treatment and PrEP programs along with the long-acting oral and injectable collaboration with Gilead. In response to the results from the MK-8507 study, Merck reviewed the white blood cell counts from their company-sponsored clinical trials involving islatravir in all indications and dosing regimens. Merck concluded that islatravir has a "dose-dependent decrease in lymphocyte counts" in a continuing phase II trial. Merck stated that the decreases were “in the normal range,” with no increase in infection related adverse events. Additionally, the company found a decrease in T-cells in participants who received the islatravir combination therapy in two Phase III studies. However, Merck found no increase in infections.