Scientists Question Clenbuterol Regulations

The drug was the focus of a National HBPA forum July 13 in Minnesota.

Scientific and regulatory advisers to the National Horsemen's Benevolent and Protective Association July 13 expressed concerns over the proposed withdrawal time and testing level for the bronchodilator clenbuterol, and they warned horsemen of potential pitfalls should the regulations be adopted.

Clenbuterol was the topic of a medication forum that was part of the National HBPA summer convention in Shakopee, Minn. The drug, considered therapeutic, has been subject to different administration times and testing levels depending on the jurisdiction, thus the effort by the Racing Medication and Testing Consortium and Association of Racing Commissioners International to push for uniform guidelines.

Dr. Steven Barker, chemist for the Louisiana State Racing Commission, said the proposed 14-day cutoff for administration, threshold of 140 picograms per milliliter in urine, and "limit of detection" in plasma are potential minefields for horsemen. Barker said scientific research has shown clenbuterol can be detected at 14 days–even 30 days in some cases–in horses, or not be detected within three days of administration in other horses.

"There is a lot of variability in the levels being seen," Barker said. "Is this a defacto ban on clenbuterol? I'd be scared to hell to use it."

Barker, as he has been in the past, was critical of the RMTC, which he said will only provide the scientific basis for its clenbuterol regulation to those who sign a confidentiality agreement. Barker said that as a regulatory chemist, he needs to defend regulators or horsemen in court and therefore requires the documentation.

"Good scientists would not want to keep good information secret," Barker said. "It's not a scientific document, it's a political document–that's shocking. We can't get information on how they established the threshold level. The defense (in a legal case) is going to attack this, and they should.

"States are rushing to adopt this without asking any questions. My question is, 'How much is based on science, and how much is based on something else? If you don't demand (information), I feel sorry for you. This is going to create more positives, not less."

Dr. Thomas Tobin, who works at the University of Kentucky Gluck Equine Research Center and serves as a National HBPA adviser, said he found "unusual aspects" of urinary excretion and detection of clenbuterol in horses in the late 1990s at about the time the drug was legalized in the United States. He said here was a spike in clenbuterol in a horse's system at 10 days.

"I would suggest that this data be made available for independent review," Tobin said.

Dr. Don Shields, a California-based veterinarian, said he collected anecdotal information from vets and trainers on clenbuterol, which currently cannot be used in a Thoroughbred within 21 days of a race under order from the California Horse Racing Board. Shield said his survey produced a mixed bag: some horses had no change, some had decreased energy levels, and others had respiratory ailments.

"It depends on who you talk to how the answers come out," Shields said.

Shields also said research shows that an increase in anabolic activity is more prevalent in Quarter Horses than Thoroughbreds. The CHRB banned the use of clenbuterol in Quarter Horses.

"Large doses (of clenbuterol) are needed for muscle changes," Shields said. "We had just assumed it happens in all doses, but it doesn't."

Dr. Robert Stenbom, equine professional services veterinarian for Boehringer Ingelheim Vetmedica, which produces clenbuterol as Ventipulmin syrup, said though the Federal Drug Administration approved its use in 1998, the drug was available for the previous 15 years in other countries. He noted it was used illegally in the U.S.

"This drug already had a huge cloud over it," Stenbom said. "And this latest one is not passing quickly. We may be under it for a very long time."