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Keywords:

  • Anticholinergic therapy;
  • Bronchodilatation;
  • Heaves;
  • RAO

Background

Equine recurrent airway obstruction (RAO) is characterized by airway inflammation, bronchoconstriction, and increased mucus production in the airways. Anticholinergic drugs like atropine induce bronchodilatation and rapid improvement in lung function. N-butylscopolammonium bromide (NBB) is an anticholinergic drug used to relieve spasmodic colic in horses, but its effect on airway smooth muscle is unknown.

Objective

To evaluate the effect of NBB on clinical signs and lung function of RAO-affected horses.

Animals

Nine horses diagnosed with RAO.

Methods

Double-blind, placebo-controlled, randomized crossover trial. Horses were challenged with moldy hay until a maximum change in transpulmonary pressure (∆PLmax) > 15 cmH2O was achieved. NBB (0.3 mg/kg) or placebo (0.9% saline) was administered IV. Clinical scores and lung function were recorded at baseline and then periodically after treatment administration. Horses were allowed a 6-week washout before administration of opposite treatments.

Results

Clinical score at 10 and 30 minutes (8.7 ± 2.8 and 8.7 ± 3.2, respectively) after NBB administration was significantly lower than baseline (10.8 ± 2.4). NBB administration resulted in a significant decrease in ∆PLmax (baseline: 35.1 ± 6.9 cmH2O) starting 2 minutes after administration (16.3 ± 6.6 cmH2O) with a maximum decline observed at 10 minutes (13.5 ± 7.1 cmH2O). ∆PLmax values between 60 and 120 minutes after NBB administration were not different from placebo.

Conclusion and Clinical Importance

N-butylscopolammonium bromide is a potent bronchodilator, reaching maximum effect 10 minutes after intravenous administration. This effect dissipates within 1 hour of drug administration.