Particulate problem prompts hold on 10 Gilead studies of HIV hopeful lenacapavir

A second major HIV prospect has been put on hold, this time from Gilead Sciences. But unlike the recent halt on Merck's drug islatravir, which was related to a drop in trial patients' immune cell counts, Gilead's trial stop stems from a quality issue that could be swiftly resolved, one analyst says.

The FDA slapped a clinical hold on 10 studies of Gilead's injectable HIV candidate lenacapavir, citing concerns about the compatibility of the solution with the borosilicate vials it's stored in. There's a risk that the borosilicate vials could interact with the drug to create "sub-visible" glass particles in the lenacapavir solution, Gilead said late Tuesday. 

The hold doesn't extend to trials of oral lenacapavir, Gilead said. As far as the injectable formulation is concerned, Gilead remains confident in the drug's future and is "committed" to sorting out its vial quality glitch "in a timely fashion," Merdad Parsey, M.D., Ph.D., Gilead's chief medical officer, said in a statement. 

“During the clinical hold, screening and enrollment of study participants and the dosing of injectable lenacapavir will not be permitted across all lenacapavir studies,” Gilead said in its release. “All other study activities, including the monitoring of participants and the dosing of participants in comparator arms, will continue according to the relevant study protocol,” the company continued.

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The affected studies range from early- to late-stage development, including two phase 3s which are now on hold. 

While the news is certainly a "setback," there's reason to believe Gilead could quickly get its injectable lenacapavir program back on track, RBC Capital Markets Brian Abrahams wrote in a note to clients Wednesday. 

First, most of the studies swept up in the hold are early and only represent a "small" market opportunity, "which even with a skipped dose … should still yield interpretable results," Abrahams said. The exception would be the two phase 3 preexposure prophylaxis (PrEP) studies, he pointed out. 

Meanwhile, dosing in the more advanced studies happens every six months. That means Gilead could sort out the vial problem quickly enough to avoid having to give many patients an alternative treatment, Abrahams said. 

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The situation could've been much worse. Just ask Merck, which last week received 13 clinical holds on its investigational compound islatravir. Seven of the 13 holds in that instance were phase 3 trials, highlighting just how significant the blow was. 

Merck said the FDA's decision stems from a concern with white blood cell counts in patients who took the drug rather than a quality issue like Gilead's.

Meanwhile, this isn't Gilead's first bout of particulate panic this month. In early December, the company said it was recalling two lots of the COVID-19 antiviral Veklury, also known as remdesivir, after a customer complaint flagged the presence of glass particulates in the injectable. Gilead confirmed the complaint through its own investigation, the company said at the time. 

Gilead didn't say how the particulates emerged in the Veklury vials, and it's not immediately clear whether the problem with lenacapavir is related.