Merck Testing a New Class of Antidepressant

Merck & Co. said Wednesday that it is developing a new antidepressant that would compete with such drugs as Prozac.

The drug, code-named MK-869, is in early human trials and is being tested for treatment of depression, schizophrenia, bipolar illness and anxiety disorder.

Unlike Eli Lilly & Co.’s Prozac and Pfizer’s Zoloft, which boost levels of the chemical messenger serotonin in the brain, Merck’s drug is a so-called Substance P antagonist.

Similar compounds have been tested for years to treat a number of ailments, including asthma. But no drug containing a Substance P antagonist has ever been approved by the Food and Drug Administration. Substance P is a chemical messenger in the brain, like serotonin.

Merck Research Laboratories President Edward Scolnick said the company has discovered that the new oral drug, which is taken once a day, acts on the brain in a different way from any other antidepressant.

“It is a totally novel breakthrough discovery in mental health,” Scolnick said. “I believe it will open up major areas of research in the four classes of illnesses that plague mental health.” Those are schizophrenia, bipolar illness, anxiety disorder and depression.

A six-week trial has shown fewer patients experience side effects with the drug than patients on serotonin boosters. Those side effects include nausea, insomnia, anxiety and sexual dysfunction. Animal studies show the drug is more effective in combination with a serotonin booster than either drug is separately.

In the U.S., the cost of treating depression totals more than $40 billion per year, according to Merck.

Shares of Whitehouse Station, N.J.-based Merck rose $2.88 to close at $98 on the New York Stock Exchange.

Depression affects an estimated 10% to 25% of American women and 5% to 10% of men at some point during their lifetime.

Dr. Donald Robinson, an independent pharmaceutical consultant in Melbourne, Fla., said that as good as antidepressants are today, “there’s still room for improvement.”

“There are some troubling side effects even with the quality of antidepressants we have today. That’s an interesting and potentially important advantage” of the Merck drug.

The company did not offer a timetable for when the drug might be introduced. But because it is in the early stages of development, it is not likely to be on the market before 2001 or 2002.