A once-a-day pill that combines three medicines for people with HIV has been approved in the U.S.

The pill, called Atripla, is a more convenient form of the pills people with HIV take to keep the virus in check.

Since the virus can become resistant to drugs when people skip pills or take medications at the wrong time, the combination treatment may help slow emergence of resistance.

"It's one thing to have medicine available, but it will only be effective when people can indeed take it as they are supposed to," U.S. Food and Drug Administration Deputy Commissioner Murray Lumpkin told reporters.

Atripla combines Viread (tenofovir), and Emtriva (emtricitabine), made by Gilead Sciences Inc., and Bristol-Myers Squibb Co.'s drug Sustiva (efavirenz).

The three drugs work to suppress HIV by blocking an enzyme the virus needs to replicate.

People with AIDS may still need to take other drugs to ward off infections and complications.

Atripla should be available in the U.S. in one week, the drugmakers said.

A month's supply will cost about $1,150 US.

Atripla's side-effects may include abnormal dreams, hallucinations and kidney problems. It can also cause birth defects.

Last month, the FDA approved another three-drug combination of generics to treat HIV in poor countries.