Trimetoquinol: bronchodilator effects in horses with heaves following aerosolised and oral administration

Reason for performing study: The bronchodilator effects of trimetoquinol (TMQ) have been studied when administered i.v. or intratracheally, but not in an aerosolised form. Objectives: To define the relationship between the therapeutic and adverse responses (therapeutic index) of TMQ when administered as an aerosol or by the oral route. Methods: Increasing doses of TMQ were administered to horses with heaves as an aerosol and by the oral route. Dose ranged 100-1000 mu g/horse for aerosolised TMQ and from 6-60 mu g/kg bwt for the oral route. Airway and cardiac effects were assessed by measurement of maximal change in pleural pressure (Delta Pplmax) and heart rate (HR), respectively. Side effects of sweating, agitation and muscle trembling were scored subjectively. Duration of action of aerosolised (1000 mu g/horse) and oral (6-60 mu g/kg bwt) TMQ was evaluated over 6 h. Results: Aerosol administration of TMQ caused dose-dependent bronchodilation but did not change HR or cause other observable side effects. When 1000 mu g/horse was administered via aerosol, TMQ produced a 2-phase bronchodilation; an immediate effect lasting up to 30 min and a second phase between 2 and 4 h. Oral TMQ was therapeutically ineffective. Conclusion: Aerosol administration of TMQ is a safe and effective method of producing bronchodilation in horses.