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

Pharmacokinetics of clenbuterol hydrochloride, salbutamol plus ipratropium bromide administered by nebuliser to horses. (130275)

Glenys K Noble 1 , Adam Cawley 2 , Himasha Mendis 2 , Cheka Kehelpannala 2 , 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

Equine asthma (EA) refers to allergic respiratory conditions characterized by airway inflammation, excess mucus formation and bronchospasm. Directly delivering bronchodilation and anti-inflammatory therapy as inhaled drugs provides pharmacotherapy and reduces the likelihood of adverse systemic effects. Clenbuterol (Clen), salbutamol (SBM) and ipratropium (IPB) administered as an aerosol is effective in the treatment of EA.

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 Clen, 1 µg/kg BW SBM and 5.5 µg/kg BW IPB twice daily for 5 days using a Flexineb E2® nebuliser.

Blood samples were taken just prior to daily drug administration to determine if there was accumulation of drugs over 5 days. Plasma was analysed for each drug using HPLC-MS/MS and results analysed using Phoenix WinNonLin software.

There was no accumulation of Clen, SBM or IPB over the treatment period. All three drugs were detected in plasma at 2 min post final administration, indicating rapid uptake of drugs from the lungs. There were statistically significant differences between mares and geldings for Tmax for Clen (0.1 ± 0.07 h v 0.53 ± 0.27 h) and Cmax for SBM (0.07 ± 0.03 ng/mL v 0.03 ± 0.01 ng/mL) and IPB (0.54 ± 0.22 ng/mL v 0.19 ± 0.10 ng/mL) as well as AUC for IPB (2.07 ± 0.66 ng/mL*h v 0.83 ± 0.20 ng/mL*h).

Plasma Clen was above the limit of quantification (LOQ = 0.025 ng/mL) at 12 h post final dose but was not detectable in any horse at 48 h. The metabolism of SBM was rapid with plasma concentrations below the limit of quantification (LOQ = 0.025 ng/mL) by 1.5 h. Similarly, IPB plasma concentrations were below LOQ (0.05 ng/mL) at 24 h after the final dose.