Seldane, a prescription drug used by millions for hay fever and allergy symptoms, can be fatal for patients with liver problems or if taken with some antibiotics or other drugs, the Food and Drug Administration warned Tuesday.
The FDA warning, sparked by recent reports of death and serious illness linked to Seldane, halted for now the company's plans to seek approval to sell the drug without a prescription.
The federal safety agency said that some patients using the antihistamine could develop an abnormal heart rhythm that could prove fatal if not treated quickly.
Marion Merrell Dow Inc., maker of Seldane, said it would immediately change the label and take other steps to warn physicians and patients of the possible dangers.
Marion Merrell stock fell $5.75 a share to $27.75 on the New York Stock Exchange, contributing to a general slide in blue chip stocks on Wall Street. Dow Chemical, which bought a majority stake in the pharmaceutical company in 1989, fell $1.875 to $53.
Seldane, the trade name for terfenadine, is extremely popular with millions of allergy sufferers because it controls the symptoms--watery eyes, itchy throat and runny nose--without causing drowsiness.
The FDA said patients on Seldane should not take the antibiotic erythromycin or the anti-fungal Nizoral, the trade name for Janssen Pharmaceutical Inc.'s ketoconazole.
Ketoconazole is used to treat vaginal yeast infections and skin fungus.
"Use of Seldane together with ketoconazole and erythromycin must be avoided," FDA Commissioner David Kessler said in a statement.
Marion Merrell said it will notify doctors and patients of evidence that the drug poses a risk for some patients of sudden heart arrhythmia, or irregular heartbeat, that can cause heart attack and death.
FDA spokeswoman Susan Cruzan said the agency had received reports of four deaths and 60 cases of sudden heart problems linked to Seldane since 1986.
The agency suspects cases involved the use of Seldane with the two other drugs.
When taken with Seldane, erythromycin and ketoconazole are thought to raise antihistamine in the blood to dangerous levels. Ketoconazole has been shown in several studies to interfere with the body's ability to metabolize, or burn up, Seldane.
Likewise, people with liver disease are at risk because their body has difficulty metabolizing the drug properly.
The agency also said that patients who take excessive doses may be putting themselves at risk. The usual dose is one 60-milligram tablet twice a day.
The company sold $768 million worth of the allergy medication last year and based on the success and apparent lack of problems intended to seek approval for an over-the-counter version.
However, Marion spokesman Dave Thomason said the company decided to "put a hold on the over-the-counter submission" pending a scientific review, which will be sent to the FDA.
Drug industry analysts said future earnings of Marion Merrell Dow may be affected because the plans to turn Seldane into a non-prescription drug are jeopardized.
The company was planning to stave off potential competition from generic drug makers when Seldane's patent expires by selling the drug over the counter, directly to consumers.
While over-the-counter sales are less profitable because of the increased marketing costs, they usually generate higher sales volume because many patients prefer not to see a physician.
Marion Merrell had record sales and earnings growth in 1991, with earnings growing at 20% for a second consecutive year. But another important drug, an anti-hypertensive drug, Cardizem, loses patent protection in November, 1992.
Prescription sales of Seldane are unlikely to be affected because doctors will be alerted to risks, said analyst Barbara Ryan at Alex. Brown & Sons. "The real issue is OTC (over-the-counter) approval," she said.
Two years ago, Marion Merrell sent warning letters to doctors on the risks of interaction between Seldane and the antibiotics erythromycin, troleandomycin and ketoconazole.