Effects of N-Butylscopolammonium Bromide on Lung Function in Horses with Recurrent Airway Obstruction

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 (∆P(L) (max) ) > 15 cm H(2) O 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 ∆P(L) (max) (baseline: 35.1 ± 6.9 cm H(2) O) starting 2 minutes after administration (16.3 ± 6.6 cmH(2) O) with a maximum decline observed at 10 minutes (13.5 ± 7.1 cm H(2) O). ∆P(L) (max) 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.