A once-daily pill that combines three drugs used to treat HIV received federal approval Wednesday, giving U.S. patients the first triple "cocktail" therapy that can be swallowed as a single dose.

The pill, called Atripla, combines three Food and Drug Administration-approved AIDS drugs that already form one of the most widely prescribed AIDS "cocktails."

Atripla can replace the two or more pills HIV-positive patients now must take each day to keep the human immunodeficiency virus in check, as well as eliminate the need for multiple co-payments when the drugs are purchased separately.

That should simplify the treatment of HIV and AIDS and in turn could slow the emergence — and ultimately, transmission — of drug-resistant strains of the virus. Those strains can evolve when patients skip pills.

"It is a major, major breakthrough for all people living with HIV and AIDS," said Frank Oldham Jr., executive director of the National Association of People With AIDS. Oldham cautioned that AIDS patients often still must take multiple other drugs to fend off infections and other complications of their weakened immune systems. Some patients also will take Atripla with a fourth drug to combat HIV.

Atripla combines Viread (tenofovir), Emtriva (emtricitabine) and Sustiva (efavirenz). Viread and Emtriva, both made by Gilead Sciences Inc. of Foster City, Calif., are now sold in combination under the brand name Truvada. Sustiva is made by New York-based Bristol-Myers Squibb Co.

The wholesale price of the new pill will be $1,150 for a 30-day supply, or the same as for Truvada and Sustiva when purchased separately. The new pill is expected to be available within seven business days.

Several initial attempts by the two companies to combine the three drugs failed. The two companies then settled on a process called "bi-layer" technology to join them in a single pill.

"The fact that innovator companies in the U.S. have actually heeded the call to collaborate on this is just an amazing happening," said Veronica Miller, director of the Forum for Collaborative HIV Research. The effort, Miller said, could lead to future collaborations on better drug combinations formulated for use in infants and children.

The FDA approved last month the first three-drug combination pill to treat HIV as part of foreign AIDS relief efforts. That combo pill, for sale only outside the United States, must be taken twice daily.

About 40 million people worldwide, including 1 million Americans, are HIV positive. Each year, roughly 5 million people are infected with HIV and 3 million die from AIDS, according to the World Health Organization.

The three drugs inhibit the replication of HIV within the body but are not a cure. Nor will the new pill be suitable for all patients: Sustiva, for instance, can cause birth defects. Serious psychiatric symptoms including severe depression, suicide attempts, aggressive behavior, delusions and paranoia also have been reported in patients taking the drug.

Gilead, Bristol-Myers Squibb and Merck & Co. Inc. intend to seek approval to sell the pill outside the U.S.

Merck, based in Whitehouse Station, New Jersey, is involved because it has rights to market one of the three drug ingredients, efavirenz, under the brand name Stocrin in many foreign countries, including most of the developing world.