RTMC revises withdrawal guidance for phenylbutazone

By: Racing Medication and Testing Consortium

Posted: March 25, 2023

The Racing Medication and Testing Consortium has been informed that the Horseracing Integrity and Safety Authority Anti-Doping and Medication Control Program has proposed enforcing the screening limit of phenylbutazone at 300 ng/mL in blood, rather than the previously established screening limit of 200 ng/mL in blood. Therefore, the withdrawal guidance will shift from 96 hours to 72 hours.

HISA will file guidance with the Federal Trade Commission that will implement the change in the enforcement of the screening limit.

The RMTC Scientific Advisory Committee has been asked by industry stakeholders to review its withdrawal guidance of phenylbutazone based on the updated proposed screening limit. In its earlier work, the Scientific Advisory Committee provided withdrawal guidance of 96 hours for phenylbutazone, which was based on a rigorous, objective process using an agreed-upon methodology given a screening limit of 200 ng/mL in blood provided by the ADMC program.

Based on the updated screening limit of 300 ng/mL in blood and a single IV dose of 4.4 mg/kg, the Scientific Advisory Committee has reviewed all available data and is now recommending an updated withdrawal guidance of 72 hours for phenylbutazone. The RMTC’s withdrawal guidance of ADMC detection times document will reflect those changes.