The logo of Gilead Sciences Inc pharmaceutical company is seen in Oceanside, California, U.S., April 29, 2020. REUTERS/Mike Blake/File Photo

March 1 (Reuters) - The U.S health regulator has declined to approve Gilead Sciences' (GILD.O) injectable drug for the treatment of HIV-1 infection over concerns related to the vials meant for the drug, the company said on Tuesday.

In a so-called complete response letter, the U.S. Food and Drug Administration (FDA) cited issues related to the compatibility of the drug, lenacapavir, with the proposed borosilicate vial.

"Gilead intends to provide FDA with a comprehensive plan and corresponding data to use a different vial type," said Merdad Parsey, chief medical officer of Gilead in a statement.

Gilead, which is also developing the drug for prevention of HIV-1 infection, plans to discuss the concerns with the agency over the coming months to work towards the drug's approval.

The issue of compatibility of the vials has been an issue since December, when some of the drug's trials, including those for prevention of HIV-1, were placed on hold by the FDA due to the potential of formation of sub-visible glass particles in the solution of lenacapavir. (https://bit.ly/3hfeXwc)

The pause was only for injectable lenacapavir. Dosing of oral formulations was allowed to continue.

Gilead's lenacapavir, meant to be injected under the skin once every six months, was developed for the treatment of patients who have undergone prior therapy and are resistant to multiple existing drugs.

Lenacapavir works by interfering with the activity of HIV capsid, a protein which protects the virus' genetic material, playing a key role in its replication.

Gilead's marketing application included data from a mid-to-late-stage trial, which showed lenacapavir, in combination with other antiretrovirals, helped reduce viral load in people living with HIV who were no longer effectively responding to their current therapy.

Gilead already has several U.S. approved HIV treatments, with Biktarvy being its top selling drug in the category, raking in $8.62 billion in 2021.

Our Standards: The Thomson Reuters Trust Principles.

Europe's medicines regulator has backed using AstraZeneca's preventative COVID-19 therapy as a treatment for the disease and also endorsed another medicine as preventative option for another common virus.

Reuters, the news and media division of Thomson Reuters, is the world’s largest multimedia news provider, reaching billions of people worldwide every day. Reuters provides business, financial, national and international news to professionals via desktop terminals, the world's media organizations, industry events and directly to consumers.

Build the strongest argument relying on authoritative content, attorney-editor expertise, and industry defining technology.

The most comprehensive solution to manage all your complex and ever-expanding tax and compliance needs.

The industry leader for online information for tax, accounting and finance professionals.

Access unmatched financial data, news and content in a highly-customised workflow experience on desktop, web and mobile.

Browse an unrivalled portfolio of real-time and historical market data and insights from worldwide sources and experts.

Screen for heightened risk individual and entities globally to help uncover hidden risks in business relationships and human networks.

All quotes delayed a minimum of 15 minutes. See here for a complete list of exchanges and delays.