Gilead Sciences has suffered a setback after regulators in the USA rejected two of the components of its four-in-one HIV drug Stribild as stand-alone therapies.

The company received complete response letters from the US Food and Drug Administration for its submissions of elvitegravir and cobicistat. The agency says that it cannot approve the applications in their current forms, noting that during recent inspections,"deficiencies in documentation and validation of certain quality testing procedures and methods were observed".

Gilead said it is working with FDA to address the questions raised in the CRLs. The two drugs are components in the once-daily single-tablet Stribild, along with emtricitabine and tenofovir, which was approved in the USA last August. The company stressed that the CRLs do not affect the marketing authorisation or continued use of Stribild.

Analysts are not too concerned about the CRLs as the drugs as monotherapies are not expected to have huge sales. However, Stribild is touted as a major  $3 billion a year blockbuster.