CLINICAL EFFICACY AND SAFETY OF CLENBUTEROL HCI WHEN ADMINISTERED TO EFFECT IN HORSES WITH CHRONIC OBSTRUCTIVE PULMONARY-DISEASE (COPD)

A field study of 239 horses was conducted to determine the efficacy an d safety of clenbuterol HCl, a beta2-adrenergic bronchodilator, when a dministered incrementally to effect in the treatment of chronic obstru ctive pulmonary disease (COPD). 'rhe severity of COPD (heaves) and res ponse to treatment was determined by clinical evaluation; an overall ' heaveiness rating' (OHR) was assigned at each observation. The horses were treated orally b.i.d. with clenbuterol (as Ventipulmin Syrup), be ginning with the lowest dosage of 0.8 mug/kg. On Day 10 of treatment a t the effective dose (0.8, 1.6, 2.4 or 3.2 mug/kg), treatment was eith er withdrawn (Schedule A) or continued for an additional 20 days (Sche dule B). Horses on Schedule A demonstrated a significant improvement i n the mean OHR on treatment Day 10 compared to the baseline overall he aveiness rating (BOHR) and a significant increase in the mean OHR (rel apse) after the drug was withdrawn. Schedule B horses showed significa nt improvement (compared to BOHR) on treatment Days 10, 20 and 30. Inc remental dosing with clenbuterol provided clinical improvement in 75% of the horses with a lower 95% confidence limit of 71%. Twenty-five pe rcent were nonresponders. A greater percentage of the more severely af fected horses required the 3.2 mug dosage or were nonresponders compar ed to horses with a lower BOHR. Side effects of sweating, muscle tremo r, and nervousness were of low intensity (mild to moderate) and freque ncy (<7% of all observations) due to the regimen of incremental dosing to effect.