Gilead Sciences Inc. said Andrew Cheng is stepping down as chief medical officer Sept. 7 to pursue another opportunity.

Cheng, who was appointed to the current role in March, has served the company since 1999 and led the development of programs in HIV/AIDS.

The drugmaker named Gregg Alton as its chief patient officer, effective immediately. Alton will facilitate access to the company's medicines and increase focus on reaching patients in the newly created position.

He joined the Foster City, Calif.-based company nearly 20 years ago and was the architect of its access program, which has enabled Gilead's HIV medicines to reach more than 11 million people in the developing world, the drugmaker said in a statement.

Meanwhile, the company also promoted its vice president of clinical research, Diana Brainard, to serve as senior vice president of HIV and emerging viral infections.

Brainard joined Gilead in 2010 and helped the company achieve regulatory approval for four hepatitis C therapies in less than four years, Gilead said in a statement.