Poster Presentation 24th International Conference of Racing Analysts and Veterinarians 2026

Determination of urinary concentrations of clenbuterol hydrochloride, salbutamol plus ipratropium bromide administered by nebuliser to horses. (130277)

Glenys K Noble 1 , Adam Cawley 2 , Himasha Mendis 2 , Cheka Kehelpannala 3 , David Batty 2 , Colin J Scrivener 1 , Jaymie Loy 1
  1. School of Agricultural, Environmental and Veterinary Sciences, Charles Sturt University, Wagga Wagga, NSW, Australia
  2. Racing Analytical Services Ltd, Flemington, Victoria, Australia
  3. Australian Racing Forensic Laboratory,, Sydney, NSW, Australia

To describe the urinary excretion of a recognised treatment for equine asthma, ten Thoroughbred horses (5 geldings, 5 mares, mean age: 11.1 ± 3.2 years; mean body weight 580.2 ± 40.4 kg) were administered a combined dose of 0.3 µg/kg BW clenbuterol (Clen), 1 µg/kg BW salbutamol (SBM) and 5.5 µg/kg BW iptratropium bromide (IPB) twice daily for 5 days using a Flexineb E2® nebuliser.

Urine was collected by free void just prior to the morning dose to determine if there was drug accumulation over 5 days. On the last day of treatment, urine was collected just prior to dosing, then every 2 h to 12 h, every 12 h from 24 h to 72 h, and daily to 168 h. All samples were analysed using HPLC-MS/MS. Descriptive statistics were calculated using SigmaPlot V13.0.

There was no increase in the urinary concentrations of Clen, SBM or IPB over the treatment period with large variations between horses and between days. All drugs were detected in urine at 2 h post-final dose.

Urinary Clen remained above the limit of quantification (LOQ = 0.05 ng/mL) to 120 h for all horses and above the limit of detection (LOD = 0.02 ng/mL) out to 168 h, with 1 mare and 2 geldings still above the LOQ at 168 h. 

There was no detectable SBM in urine of any gelding after 72 h with similar findings in mares. However, SBM was detected in one mare below the LOQ (0.05 ng/mL) but above LOD (0.02 ng/mL) at 120 h. No SBM was detected in any horse from 144 h onwards.

There were detectable concentrations of urinary IPB in both mares and geldings above the LOQ (0.05 ng/mL) at 168 h after the final dosing. Only one gelding had no detectable (<0.02 ng/mL) IPB at 168 h.