Pfizer is celebrating after advisors to US regulators unanimously endorsed the firm’s Celsentri for approval, which should make it the first new type of HIV/AIDS treatment to hit the market in more than a decade.

The US Food and Drug Administration will now look in June at its Antiviral Drugs Advisory Committee’s recommendation to give the go-ahead to Celsentri (maraviroc), which will be the first in a new class of HIV/AIDS treatments called CCR5 antagonists to be approved. Rather than fighting HIV inside white blood cells, the drug prevents the virus produced by infected cells from entering uninfected cells by blocking its predominant entry route, the CCR5 co-receptor.

The committee said that maraviroc provides an alternative for 25,000-40,000 people in the USA who are unable to treat their disease with currently available drugs, and the benefits outweigh the risks of liver damage and infections. However the advisors have recommended that Pfizer conduct additional tests to assess side effects and the drug's effectiveness on a broader population than has already been tested. In the company's clinical trials submitted to the FDA in support of its Celsentri New Drug Application, 90% of the patients were male and 83% were Caucasian.

It is debatable how big an earner Celsentri is likely to prove for Pfizer. 25,000-40,000 patients is a fairly small subset to be starting with and patients will have to take a diagnostic test to determine if they have the version of the HIV virus appropriate for treatment with Pfizer's drug. The only test currently available is manufactured by Monogram Biosciences. However the New York-based drugs giant said maraviroc would likely be used initially for treatment-experienced patients, but its label could eventually be expanded for newly-diagnosed sufferers.

Analysts have estimated peak sales of $200-$500 million but say that much will depend on the progress of Merck & Co’s rival product, the integrase inhibitor Isentress (raltegravir), formerly known as MK-0518. Merck anticipates filing its HIV drug with US regulators by the end of the second quarter this year, for patients who are resistant to older treatments.