By Justin Gillis
Washington Post Staff Writer
Tuesday, April 21, 1998; Page C1

Enthusiasm about a new treatment for sexual impotence drove the shares of Pfizer Inc. to an all-time high in brisk trading yesterday. At day's end, it ranked as the top U.S. drug company in stock market value, passing Merck & Co.

Analysts variously estimated that doctors are writing 15,000 to 40,000 new prescriptions a day for Viagra, Pfizer's $10-a-dose pill against impotence. Even if the lower number is correct, Viagra could turn out to be one of the most successful product launches in pharmaceutical history.

Viagra was licensed by the U.S. Food and Drug Administration on March 27, and has been on pharmacy shelves in most parts of the country for about a week. Most previous treatments involved creams, implants or injections. Urologists and other doctors who treat impotence say that men who have never talked about their problem are coming out of the woodwork to demand the pill.

"They're calling in on a daily basis," said Harold Bondy, an Arlington urologist who has already written about 20 prescriptions. "They basically have heard about the tablet and they want to try it."

Positive news about Viagra's sales drove Pfizer's stock price to a record $113.75 in trading on the New York Stock Exchange yesterday, though by the close the stock had fallen a bit, to $113.37 1/2. That was a jump of nearly 8 percent from Friday's close.

Yesterday's trading volume exceeded 10 million shares, three times the volume on a typical Monday. Pfizer's stock has been gaining for weeks amid speculation about Viagra, and is up 30 percent since early March.

At the closing bell, the stock market valued the shares of Pfizer, based in New York, at about $147 billion, approximately $1 billion more than the market value of the previous leading drug company, Merck, of Whitehouse Station, N.J.

Merck is a larger company in sales and profits, having earned $4.6 billion on sales of $23.6 billion last year, compared with Pfizer's $2.2 billion in net income on sales of $12.5 billion.

Urologists say they are generally optimistic about Viagra as a drug, but some are also a little worried. It is plainly effective for some patients and, in research studies, the side effects were generally mild. Yet Viagra is so new that nobody knows yet what side effects will emerge when it is used by millions of people. It is not a cure-all, and doctors fear the rush to embrace it may obscure serious medical problems for which impotence has traditionally been a warning sign.

True clinical impotence is often a sign of problems with blood vessels caused by diabetes, a potentially life-threatening disease if not treated properly. Impotence can also be a tip-off to heart disease, prostate cancer or a particular kind of brain tumor. It can result from a low testosterone level, a simple and easily treated problem.

A good doctor will rule out such underlying causes, or get a handle on them, before sending a patient off to the drugstore.

That hasn't stopped quacks who detect a potential bonanza in Viagra. Already, some clinics are advertising on the Internet and in the backs of sex magazines, offering to charge a credit card $50 or $75 and send out a Viagra prescription in the mail, no questions asked and no examination required.

"If you go ahead and give somebody a treatment and he turns out to have a brain tumor, you're not helping him," said Yousef Salem, an Alexandria urologist. "I suspect that if no proper work-up is done and the prescriptions are given randomly, some may die."

Pfizer has condemned indiscriminate use of its drug and has urged any man who wants to try it to seek competent medical care. At the same time, the company is hardly displeased by the wave of sales that Viagra is generating.

"We've been saying that erectile dysfunction is a major unmet medical need," Pfizer spokesman Andy McCormick said yesterday, so Pfizer welcomes the drug's popularity.