Functional response to inhaled salbutamol and/or ipratropium bromide in Ascaris suum-sensitised cats with allergen-induced bronchospasms

Knowledge about the use of inhaled bronchodilators in cats with so-called 'feline asthma' is limited and relies on the experience of clinicians treating these patients. A randomised controlled four-way crossover study was therefore designed to compare the effects of salbutamol (SAL, 100μg), ipratropium bromide (IB, 20μg) and a combination of both (SAL/IB, 100μg/20μg), delivered through a pressurised metered-dose inhaler (pMDI) connected to a spacing chamber, on allergen-induced bronchospasms in five Ascaris suum (AS)-sensitised cats. Four AS bronchial provocation challenges were carried out at 1week intervals, followed by one of four treatment protocols: SAL, IB, SAL/IB or control (untreated). Enhanced pause (Penh), an estimator of airflow limitation measured by barometric whole-body plethysmography, was repeatedly assessed within 120min following the administration of each treatment protocol. Responses to inhaled medications were evaluated by calculating the area under the time-response curves (AUC) from 0 to 60 or 120min after drug administration (AUC_0-60, AUC_0-120), as well as the times required for half-recovery (T_50%) or for returning to nearly basal conditions (T_20%). No significant differences were found among the four study groups, with reference to the mean AUC_0-60, T_20% and T_50% values of Penh (P>0.05). Mean AUC_0-120 values of Penh were similar between the bronchodilators tested, but were significantly lower than those in the untreated group. It was concluded that inhalation of SAL, IB and SAL/IB via pMDI failed to improve most Penh-derived parameters, which suggested that these bronchodilators were of limited efficacy in reversing allergen-induced bronchospasm in cats. However, further studies using a larger number of animals are warranted to investigate if different drugs or delivery devices or higher dosages may be more effective.