Pfizer, Schering HIV Drugs May Fail On Incorrect Test

(Bloomberg) -- Pfizer Inc.'s new AIDS drug and a similar pill from Schering-Plough Corp. may stop working in some patients because a test identifying who should get the medicines is sometimes inaccurate.

The pills, made by Pfizer, of New York, and Schering, based in Kenilworth, New Jersey, block a chemical entryway known as CCR5 that the virus uses to infect cells. In about 10 percent of cases, a Monogram Biosciences Inc. test incorrectly identifies patients who will benefit from the drug, scientists said this week at an AIDS meeting.

New research on Pfizer's Selzentry and Schering's vicriviroc, as well as the test's reliability, will be presented today at the Conference on Retroviruses and Opportunistic Infections in Boston. While the pills promise to fight HIV in patients who can't take older medicines, the new drugs' effectiveness depends on accurate screening.

``The test is wrong in about 8 to 10 percent of patients initially screened to see if they are candidates for a CCR5 antagonist,'' David Hardy, director of the division of infectious disease at Cedars Sinai Medical Center in Los Angeles, said in a telephone interview. ``We're waiting to see if the next-generation test from Monogram will eliminate the errors.''

Selzentry was cleared in August for patients who stopped responding to older medicines. It's the only approved CCR5 inhibitor, the first new family of AIDS medicines in a decade.

Pfizer didn't report revenue for Selzentry last year. Analysts have projected the pill could have peak annual sales of about $300 million. Vicriviroc, a similar drug, is in the third and final stage of testing usually required for U.S. regulatory approval.

90 Percent

As many as 90 percent of previously untreated HIV patients will have a strain of the virus that enters healthy cells through the CCR5 doorway, Howard Mayer, executive director of clinical research and development for Pfizer, said in an interview at the meeting in Boston.

After five years of HIV infection, about half of patients still have that strain, Mayer said. By then, most patients have higher levels of another virus version known as X4 that infects cells through a different route unaffected by drugs such as Selzentry and vicriviroc.

A new test to better determine who can benefit from the Pfizer and Schering drugs is about six months from reaching the U.S. market, Chris Petropoulos, chief scientific officer for South San Francisco-based Monogram, said in a telephone interview.

 

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