A Florida pharmacy acknowledged Thursday that it had incorrectly mixed a medication given to the 21 polo horses that died Sunday at the United States Open Polo Championship, even as state and federal authorities waited for the results of a toxicology test that would determine the cause of the horses’ deaths.

Jennifer Beckett, the chief operations officer of Franck’s Pharmacy in Ocala, Fla., said in a statement that the strength of an ingredient in a medication mixed at the request of a veterinarian was incorrect, and that the pharmacy had notified the state’s health department.

Although Beckett did not name the ingredient or the medicine, a statement released to The Associated Press on Thursday by the polo team, Lechuza Caracas, indicated that a team veterinarian had ordered a vitamin mixture similar to Biodyl, a supplement that is not approved by the Food and Drug Administration.

Despite the revelations Thursday, a spokeswoman for Florida’s Department of Agriculture said investigators had not identified a cause of death and were awaiting the results of a toxicology test. Spokeswomen for the F.D.A. and the Florida Department of Health declined to comment, saying the investigation had not been completed.