Bapten, a medication that has shown promise in the treatment of bowed tendons, has been taken off the market because of reports of a troubling side effect. A prepared statement from Boehringer Ingelheim, the pharmaceutical company that distributes the drug, described the suspension of sales as “temporary.”

According to the statement, the action was prompted by “some observations of tendon swelling” in horses that have received Bapten.

“This ‘stop sale’ is voluntary; we weren’t told by anyone to do it,” Allyn Mann, equine products manager for Boehringer Ingelheim’s Animal Health Division, said Dec. 7. “There is a package insert that comes with the drug that talks about adverse reactions and the fact that tendons can swell up. However, more (swollen tendons) than what we would consider a comfortable number have been reported.”

Bapten was approved for use in horses by the Food and Drug Administration earlier this year after more than seven years of research, including FDA-regulated field trials at universities and various other sites across the country. In a study that was presented at the 1997 American Association of Equine Practitioners convention last December in Phoenix, Ariz., more than 60% of the injured horses treated with Bapten were able to return to competition and 50% were able to race at least five times. Only 33% of the horses that received a placebo were able to return to competition and race at least five times