Two of the world's biggest drugmakers spun off last week their divisions that manufacture AIDS drugs and combined them into one company focusing on the disease.

The new company, ViiV Healthcare, will initially be 85 percent controlled by GlaxoSmithKline and 15 percent controlled by Pfizer. With headquarters in London, the company initially has a portfolio of 10 licensed drugs, including some of the earliest, such as AZT and lamivudine, and later ones, such as maraviroc, with combined sales of about $2.7 billion in 2008. It also has seven drugs in the pipeline.

The companies say they will try to develop new drugs and new formulations of current ones, such as combination doses for children. ViiV Healthcare will also seek partnerships with other companies to develop multidrug cocktails.

But Mark Harrington, executive director of the Treatment Action Group and a longtime AIDS activist, was skeptical. Harrington said he worried that separating AIDS work from the larger companies could result, for example, in too little money for a big clinical trial. And the mergers of the last decade meant fewer scientists assigned to AIDS research.

"We'd love to be proved wrong," he said, "but we're worried that fewer companies in the field could mean innovation is slowed down."