Merck Discloses Human Tests of 2 AIDS Drugs : Medicine: The compounds have been shown to inhibit HIV in the test tube. The trials are to determine tolerability and safety in people.

Merck & Co., the world’s largest pharmaceuticals company, has begun preliminary human testing of two closely related potential compounds for use against AIDS.

Merck, which is traditionally tight-lipped about drugs so early in the testing process, acknowledged the trials in response to inquiries from investors, Linda Distlerath, senior director of science and technology policy, said Friday.

In composite trading on the New York Stock Exchange Friday, Merck closed at $87.625, up $1.50 on volume of 1.7 million shares.

The drugs--known internally by Merck as L-697,639 and L-697,661--are members of a class known as reverse transcriptase inhibitors. Reverse transcriptase is an enzyme that is crucial to the reproduction and growth of HIV, the human immunodeficiency virus that is believed to cause AIDS.

“Our scientists came upon these drugs after screening some 23,000 other compounds against HIV,” Distlerath said.

Although the drugs were sped from the test tube to humans in a bit more than six months--most drugs take two years--Distlerath cautioned that four of five drugs at this stage of research fail.

The preliminary human tests, known as Phase I trials, are being conducted at an undisclosed site in Europe and began this week at the National Institutes of Health in Bethesda, Md. Phase I studies are designed to determine the safety, tolerability and absorption of potential compounds.

The compounds have already been shown effective against HIV in test tubes and in cultured human cells, and nontoxic in rats and monkeys.

Margo Warren, a spokeswoman for the NIH, said 40 HIV-infected individuals without symptoms have been entered into the study.

Martin Delaney, executive director of Project Inform, a patient advocacy group in San Francisco, said he is “encouraged that a company with the resources of Merck is choosing to work in this field.”

Still, he added, “we’ve all learned to be cautious about new drugs this early in the research cycle.”

Merck, of Rahway, N.J., is also a contender, along with SmithKline, Upjohn, and Hoffman-LaRoche, in the race to develop another class of antivirals, known as protease inhibitors, for use against HIV. And Janssen Pharmaceuticals is developing another class of anti-HIV agents known as TIBO derivatives.

Burroughs-Wellcome’s drug AZT, the only compound licensed for use against HIV, also interferes with reverse transcriptase but in a significantly different manner from the new Merck compounds. DDI and DDC, made by Bristol-Myers Squibb and Hoffman, respectively, are chemical cousins of AZT.