AIRWAY RESPONSE OF HORSES WITH COPD TO DRY POWDER INHALATION OF IPRATROPIUM BROMIDE

To determine the effects of the dry powder inhalation (DPI) of ipratro pium bromide (ipratropium) on the airways of healthy horses and the do se-response curve in horses suffering from chronic obstructive pulmona ry disease (COPD) by means of pulmonary function tests, five healthy h orses were first studied. Ipratropium (2400 mu g ipratropium horse(-1) ) was contained in gelatine capsules and administered using a dry powd er device connected to an adapted face mask. Pulmonary function tests were recorded before inhalation and 15 and 60 min after inhalation. No modification of pulmonary function was observed. The airway response to ipratropium DPI was then determined in six horses suffering from CO PD. To induce airway obstruction, the horses were bedded on straw and fed hay. When the maximal change in pleural al pressure during tidal b reathing exceeded 1.96 kPa, pulmonary function tests were recorded bef ore DPI, and 15 and 60 min post-inhalation. Placebo (six capsules hors e(-1)) or ipratropium (600, 1200 and 2400 mu g horse(-1)) was administ ered in a randomized order to each horse using the dry powder device a nd the adapted face mask. Neither ipratropium nor placebo DPI affected respiratory frequency (f) or tidal volume (V-T). Inhalation of 600 mu g ipratropium horse(-1) resulted in a delayed decrease of total pulmo nary resistance (R-L) whereas dynamic compliance (Cdyn) was improved ( although not significantly) at both times of measurement when compared with values following placebo inhalation. Simultaneous decreased R-L and increased Cdyn, was observed within 15 min after DPI of 1200 mu g ipratropium horse(-1) and persisted for the 1 h duration of the experi ment. Doubling the dose also improved pulmonary function but not signi ficantly more than following inhalation of 1200 mu g ipratropium. No s ystemic side effects were observed in either group of horses.