'Pfizer does have a huge and growing pipeline,' said a spokesman. 'When we last gave an update we talked about 222 development programs ... and it's grown by 20 percent in two to three years. You do expect some of those to not reach the market, but this is a risky business.'

Pfizer said it dropped developing the capravirine HIV drug because two mid-stage studies failed to show that it significantly helped patients. Specifically, the drug did not boost the effectiveness of standard triple-drug HIV therapies in patients who had failed to respond to available antiretroviral therapies, the New York-based drug maker said.

The company will return rights to the compound to its developer, Shionogi & Co. of Japan.

Pfizer is left with one HIV treatment in late-stage studies, a drug called maraviroc that is designed to block HIV from entering cells.

Primary Targets

Separately, Pfizer ended a collaboration with Altana on its Daxas drug, a treatment for asthma and a lung disorder that is usually caused by smoking. Altana said early Friday that while the drug significantly improved lung function in patients with chronic obstructive pulmonary disease, it did not reduce the accompanying shortness of breath or lasting cough. The company had set both of these measures as primary targets.

Pfizer is returning all rights to Daxas to the Bad Homburg-based company, which said it will continue development and foresees no delay in US clinical trials of the therapy.

Last year, Altana delayed its application for US approval of Daxas, and said slow patient recruitment was hampering the process. A number of similar products are currently in development by rivals and there is competition for patients for the necessary trials.

'Risky Business'

Pfizer spokesman Stephen Lederer said the company has not disclosed any other treatments in its pipeline for the lung disorder.

"Pfizer does have a huge and growing pipeline," Lederer said. "When we last gave an update we talked about 222 development programs ... and it's grown by 20 percent in two to three years.

"You do expect some of those to not reach the market, but this is a risky business."