The Food and Drug Administration have rejected two of Gilead Sciences Inc. HIV drugs as standalone therapies. The FDA cited deficiencies in documentation and validation of certain quality testing procedures as the reason for rejection.

According to CBS News Gilead Sciences Inc. received a rejection letter from the FDA and has since been working with them to address the questions that were raised in the letter in order to move the process of approval forward.

The announcement was made by the pharmaceutical company on Monday. The FDA previously approved ingredients used in Gilead Sciences Inc. pill Stribild back in August 2012.

Like most other HIV drugs, Stribild carried a boxed warning about potentially dangerous side effects, which include nausea and diarrhea.

According to Reuters the company is seeking approval for its drug elvitegravir for people with HIV who have already been treated with other products. "The drug blocks the enzyme integrase which is needed for the HIV virus to replicate."

Gilead is also seeking approval of cobicistat, which is a drug that boosts the function of other HIV medicines rather than fights the virus itself.

Both drugs are already contained in Gilead's once-daily single-tablet HIV treatment Stribild, which combines four different medications

Analysts on average expect elvitegravir, if eventually approved, to generate annual sales of about $300 million by 2016 according to Thomson Reuters' data. They expect sales of cobicistat if approved to produce roughly around $242 million over the same period.