Undated (AP) _ Seldane was marketed as an answer to a prayer. It relieved the allergy symptoms of wheezing, sneezing, watery eyes and runny noses without the drowsiness that would keep users from driving cars or going to work.

But Vera Spivey stopped taking it. On Monday, the Food and Drug Administration directed the maker of the popular prescription drug to warn doctors and patients that Seldane can cause lethal heart problems if taken in combination with two other medications.

''It frightened me. I decided to put it in the medicine cabinet for a while. I want to make sure,'' said Mrs. Spivey, 43, of Fredericksburg, Va., who had a prescription filled Saturday for 60 tablets.

Doctors, however, say patients have little to worry about if they are not taking the antifungal drug ketoconazole or the antibiotic erythromycin, and if they do not have a significant liver disorder that would prevent the body from metabolizing Seldane.

''Patients can be reassured that as long as they are not taking these other medications, Seldane is an extremely safe drug,'' said Dr. Richard Lockey, president of the American Academy of Allergy and Immunology.

Lockey said letters containing that reassurance are being sent to the academy's 5,000 allergy specialists.

''It certainly is a reasonable thing to be cautious. But undue panic is really not appropriate. We're dealing with low-frequency side effects,'' said Dr. John Ohman, allergy specialist at the New England Medical Center.

''It's still a safe drug as long as it's used appropriately,'' said Dr. Terry Levine, an allergist in Overland Park, Kan., who had received about a dozen calls from patients Wednesday.

Since 1989, the FDA said there have been 64 cases of heart problems, 15 cases of heart attacks and at least four deaths involving Seldane.

It said the incidence of side-effects was low, but users of the drug should contact their doctor if they feel faint or have heart palpitations.

The FDA asked Seldane's manufacturer, Marion Merrell Dow Inc. of Kansas City, Mo., to place a warning on the label and to develop leaflets for consumers.

The company, whose stock fell more than six points after the FDA announcement, sent warnings by Mailgram to 600,000 doctors, nurses and pharmacists. The warning is stronger than a 1989 note of precaution the company sent about the use of Seldane in conjunction with the other medications.

Seldane has been on the U.S. market since 1985, and the company said about 200 million patients worldwide have taken it to ease allergy symptoms. Seldane sales were $768 million last year, the company said.

The company sold Seldane with ads that said: ''Now you can put your hay fever to sleep while you stay awake.''

About 40 million Americans suffer from upper respiratory allergies.

Marion Merrell Dow was planning to ask the FDA for permission to sell Seldane over the counter instead of by prescription, but the application has been delayed until more tests are done on its safety.

Dr. Sydney Wolfe of the consumer group Public Citizen said the new warning should prohibit use without a doctor's prescription.

''It should essentially close the door on any over-the-counter use of the drug. It's just too dangerous,'' Wolfe said.

He suggested that allergy sufferers use over-the-counter remedies that contain chlorphenaramine but take it at lower doses to prevent drowsiness.

Meanwhile, some Seldane users say they'll keep swallowing the tablets, which are especially in demand because the pollen season has been worse than normal this year.

''I live on Seldane. It really helps with my symptoms and gets me through the day,'' said Rob Wilson, a spokesman for IBM Corp. ''I'm not at all concerned about the warning because potential problems are under such limited circumstances. It won't change my habit in any way.''