Gilead Sciences' recent run of positive regulatory developments in HIV hit a setback when the FDA issued the company a complete response letter saying it could not approve the use of two medicines as monotherapies in treatment regimens.
The US regulator said it was unable to back elvitegravir and cobicistat because recent inspections had uncovered “deficiencies in documentation and validation of certain quality testing procedures and methods”.
Both drugs are part of Gilead's four-in-one combination drug Stribild that was approved by the FDA in August 2012, and is tipped for blockbuster status due to its less complicated once-daily regimen that could improve adherence.
Gilead made sure to point out that the latest FDA decision does not the marketing authorisation for Stribild, which was also approved in Europe in March 2013.
Nevertheless, the FDA decisions on elvitegravir and cobicistat will be a disappointment, and Gilead said it is working with agency to address the questions raised in the complete response letters and move the applications forward.
Elvitegravir is an integrase inhibitor that works by blocking the ability of HIV to integrate into the genetic material of human cells.
Gilead licensed the drug from Japan Tobacco in March 2005 and has exclusive rights to develop and commercialise elvitegravir in all regions, excluding Japan, where Japan Tobacco retains rights.
Cobicistat doesn't tackle the virus itself, but supports the effect of other medicines by boosting the body's metabolism.
The other two drugs that make up Stribild are tenofovir and emtricitabine. These two ingredients were approved by the FDA in July 2012 in a separate combination known as Truvada.
This product was the first licensed drug in the US that has been shown to reduce the risk of HIV infection acquired through sexual intercourse, and is recommended along with safer sex practices by people at high risk of infection as part of an HIV prevention strategy called pre-exposure prophylaxis.