With Pfizer Drug, HIV Retreats

Yesterday, at the 15th International AIDS Conference, Pfizer (NYSE: PFE  ) reported data from the drug UK-427,857, which treats HIV infection. Under a once-daily dosing regimen, the drug produced a 10- to 100-fold decline in HIV levels in the patients' blood after 10 days.

Pfizer already has two drugs for HIV on the market, though in Pfizer's portfolio of major drugs, Rescriptor and Viracept are almost an afterthought. Viracept sales have been declining in recent years from $364 million in 2001 to $259 million last year. Rescriptor doesn't even warrant a mention in the company's annual report, suggesting that sales are insignificant.

The successful development of UK-427,857 could beef up Pfizer's presence in a market that is always in need of new drugs. There is high demand for drugs like this one that work through a novel mechanism as HIV develops resistance to other types of drugs. For example, drugs such as Viracept and Lexiva from GlaxoSmithKline (NYSE: GSK  ) and Vertex Pharmaceuticals (Nasdaq: VRTX  ) work by interfering with the HIV protease enzyme, impairing the ability of the virus to replicate itself.

The strategy with UK-427,857 is to prevent the virus from even entering the cell. If it can't infect healthy cells, the virus can't replicate. In general, this approach is similar to the mechanism used by Fuzeon, from Roche and Trimeris (Nasdaq: TRMS  ) . One important difference is that Fuzeon is a peptide and is incredibly expensive to manufacture, leading to a very high and controversial drug cost. As a small-molecule drug, UK-427,857 will dodge some of the problems that have plagued Fuzeon.

A phase 3 trial with UK-427,857 is expected to begin by the end of this year. It is always a bit of guesswork to gauge drug development timelines, but it appears that if all goes well, the drug could get Food and Drug Administration approval by late 2007 or early 2008. That would be a great thing for HIV patients, and for Pfizer.

For additional Foolish perspectives on Pfizer, see:

• Pfizer Wants to Be Your Pfriend
• Diagnosing Pfizer
• Pfizer's Fight

Fool contributor Charly Travers owns shares of Vertex Pharmaceuticals.