The sport is waiting for a second Medina Spirit test result. Why is it taking so long?

Medina Spirit, who won the Kentucky Derby on May 1 to give the trainer Bob Baffert a record seventh victory in the race, was nearly excluded from the Preakness Stakes when it was disclosed that he had failed a drug test after the Derby.

Medina Spirit tested positive for betamethasone, a corticosteroid, but officials in Kentucky are awaiting results from a second sample to determine if his Derby victory will be overturned. That could have set up an awkward situation if Medina Spirit had won the Preakness, the second leg of the Triple Crown.

The results from a second sample are not expected for several weeks. So what is taking so long, and aren’t the results from a Kentucky Derby winner given priority?

Testing so-called A samples is a function of a contract between a laboratory and a state racing jurisdiction and therefore very predictable. And while testing so-called B samples is relatively easy — especially because laboratories are looking only for the substance reported by the original finding — the ability of some labs to clear previously contracted work and get to those samples can be limited, especially given that the labs do not have the state’s contract and because the trainer of the horse whose results are in question is given his or her choice of laboratories for the second sample.

Bob Baffert, Medina Spirit’s trainer, admitted on Tuesday that he was responsible for the colt’s failed drug test, saying he had used an ointment for dermatitis that he was unaware contained the drug in question. He had previously offered various theories about how Medina Spirit tested positive for 21 picograms of betamethasone. While 21 picograms per milliliter of blood seems relatively small, said Dr. Mary Scollay, executive director and chief operating officer of the Racing Medication and Testing Consortium, a horse has about 50,000 milliliters of blood, so the result is not insignificant.

While she did not treat Medina Spirit or review his results first hand, based on the administration studies that were funded by the R.M.T.C., she said, 21 picograms is consistent with the intra-articular administration of nine milligrams into a single fetlock joint less than 72 hours before sampling.

Medina Spirit and two other horses trained by Bob Baffert have cleared all of the pre-race drug tests that were a requirement for the horses to run this weekend at Pimlico Race Course.