- Due to safety concerns, Gilead and Merck & Co. have temporarily stopped enrolling patients in a key clinical trial testing two of their experimental drugs as a combination treatment for HIV.
- The decision, announced Wednesday, comes less than a week after Merck revealed that dosing had been stopped in a separate study evaluating its drug, islatravir, in combination with another therapy known as MRK-8507. The study recently found that patients who received the drugs had decreases in certain kinds of white blood cells, especially when they were on high doses of MK-8507.
- Now, out of an "abundance of caution," Merck and Gilead have chosen to hold off adding more patients to their trial as they consider making adjustments to it. The companies said they remain optimistic about the pairing of islatravir and Gilead's medicine, called lenacapavir, and that participants already enrolled will keep receiving the drugs. They will also continue to be monitored per the current protocol.
Merck's announcement last week hinted that, if there is a safety issue, it seems more likely to lie with MRK-8507 than islatravir.
While not ideal, that would surely be better for Merck than the opposite. The company has for years touted islatravir as one of its most valuable experimental programs, an asset that could one day serve as a "foundational anchor" for so-called two-drug HIV treatments.
And perhaps just as important to Merck, islatravir could provide a boost to an HIV business currently headed by the drug Isentress, sales of which fell 9% between the first nine months of 2020 and the same period this year.
As for Gilead, islatravir is a bit of a double-edge sword. The drug could create more competition for Gilead's market-leading portfolio of HIV medications. However, it might also help prop up lenacapavir, hence why Gilead opted to team up with Merck and research them together.
According to Brian Abrahams, an analyst at RBC Capital Markets, lenacapavir is a viable option for HIV pre-exposure prophylaxis, or PrEP, all on its own. But to compete in the treatment of HIV, Gilead "will likely need to combine [its drug] with another long-acting agent," the analyst wrote in a Nov. 18 note to clients.
On that front, Abrahams argues islatravir is an attractive option, as it's shown to be durable and complementary to lenacapavir in terms of side effects and resistance profiles.
However, if uncertainties surrounding Merck's drug persist, Gilead may need to look elsewhere for a combination partner, Abrahams wrote.
The choice to pause the study of islatravir and lenacapavir was a "smart move" on Gilead's part, according to Evercore ISI analyst Umer Raffat. "I think this is a very prudent decision, and it may have just saved [lenacapavir] from a worst-case outcome," he wrote in a Nov. 24 note.
Raffat wrote that HIV drugs usually aren't very successful if they cause drops in white blood cell counts like the ones seen in the MK-8507 study. So, had there been declines in the lenacapavir and islatravir trial, it could have increased scrutiny around Gilead's drug as well.
And to Raffat, declines were likely, given the dose of islatravir being used in the lenacapavir trial was significantly larger than when it's used as a daily dose.