Boehringer Ingelheim won U.S. approval on Wednesday to sell its AIDS medicine Aptivus for treating adults with drug-resistant HIV infections in combination with Abbott Laboratories Inc.‘s Norvir.

Germany’s Boehringer, the world’s largest privately held drug company, said Aptivus would begin to be available in pharmacies nationwide within two weeks.

A U.S. Food and Drug Administration spokeswoman confirmed the agency had approved Aptivus, a protease inhibitor.

Protease inhibitors help suppress the HIV virus that causes AIDS. Although there are eight protease inhibitors approved in the United States, most patients develop resistance.

Health experts say new drugs that are different enough from the old ones are needed to give patients more options.

Andreas Barner, Boehringer’s head of research, hopes for approval from European regulators in the second half of 2005.

“We would then be able to introduce the drug in the first European markets in winter. Germany and the UK will be among the first markets,” Barner said in an e-mail.

Two major clinical trials funded by Boehringer showed Aptivus, also known by its chemical name tipranavir, was more effective than other HIV drugs when used in combination with Abbott’s Norvir.

Nearly 40 percent of Aptivus/Norvir patients showed lower virus level after 24 weeks, compared with about 21 percent of those taking Abbott’s Kaletra (which is a combination of Norvir and another protease inhibitor), Boehringer has said.

In May, an FDA advisory panel cautiously supported approval of Aptivus but said more safety studies were needed on its long-term effects on the liver and cholesterol levels.

One early study showed initial liver toxicity in healthy people taking Aptivus, and later data showed 10 percent of patients taking it had liver problems compared with 3 percent on similar drugs. It also caused rashes in some women.

Boehringer said in a statement that all patients taking Aptivus should be followed closely by clinical and laboratory monitoring.

The safety and effectiveness of Aptivus is still being studied in adults who are not drug-tolerant as well as children.

Aptivus would compete with other protease inhibitors such as Roche’s Invirase, GlaxoSmithKline’s Lexiva, Pfizer’s Viracept and Merck & Co’s Crixivan.

Boehringer plans to market Aptivus on its own, Barner said. The company had more anti-AIDS drugs in development and is open to licensing drugs from other companies.