Use of a hand-held, metered-dose aerosol delivery device to administer pirbuterol acetate to horses with 'heaves'.

Aerosol administration of bronchodilators to horses is recommended for treatment of certain airway diseases such as 'heaves'. We have developed a novel, hand-held, metered-dose inhaler and we sought to determine the bronchodilator efficacy of the beta 2 adrenoceptor agonist pirbuterol delivered by this device to horses affected with 'heaves'. To induce airway obstruction, 6 heaves-susceptible horses were stabled, bedded on straw and fed hay. When the maximum change in pleural pressure during tidal breathing (delta Pplmax) was greater than 20 cmH2O on 2 consecutive days, pulmonary function was measured before and 5, 10 and 30 min, as well as 1, 2, 3, 4, 5, 6 and 7 h after administration of aerosol pirbuterol. Pirbuterol was administered using a metered canister and the hand-held delivery device that was inserted into the left nostril. Either vehicle or pirbuterol acetate (400, 600, 800, 1200 or 1600 micrograms) was administered to each horse. Relief of airway obstruction indicated by changes in pulmonary function was observed within 5 min after administration of both vehicle and pirbuterol. Significant decreases in delta Pplmax and pulmonary resistance (RL) and an increase in dynamic compliance (Cdyn) persisted for the 7 h duration of the experiment. Comparison of the effect of vehicle and pirbuterol at each time period showed that pirbuterol decreased RL and delta Pplmax significantly for up to 1 h. The optimal dose was determined to be 600 micrograms. Immediate response to treatment, magnitude of drug effect and lack of side effects indicated that aerosol pirbuterol is an effective and safe bronchodilator in horses with 'heaves'. The hand-held, metered-dose aerosol delivery device was very convenient and extremely effective and is, therefore, recommended for delivery of therapeutic aerosols to horses.