As part of its ongoing battle with drugmaker GlaxoSmithKline over the pricing of anti-HIV medications, the California-based AIDS Healthcare Foundation on Tuesday sent a letter to the Food and Drug Administration asking the agency to revoke approval of Glaxo's combination antiretroviral pill Trizivir. The request was based on a recent National Institutes of Health study showing that Trizivir is less effective than other anti-HIV combinations. Trizivir combines three Glaxo drugs--AZT, 3TC, and Ziagen--into a single pill. AHF said that based on the NIH study's findings, it's "apparent that Trizivir may be effective only if it is taken with other HIV/AIDS drugs," and it urged the FDA to remove the medication from the market because not all doctors may be aware that the combination pill is not as effective as other treatments. AHF is currently challenging Glaxo's patents on 3TC, AZT, and Ziagen--and the company's combination pills Combivir and Trizivir that contain the compounds--in federal court by claiming that the patents are invalid because basic research into the drugs was conducted with federal tax dollars. The lawsuit also claims Glaxo charges significantly more for the drugs than the company's licensing, manufacturing, and distribution costs for the medications. A Glaxo spokeswoman said the latest move by AHF to get the FDA to pull approval of Trizivir is irresponsible, noting that the NIH study did show the combination pill to be effective when used with other anti-HIV medications. An FDA spokesman said the agency plans to review AHF's request.