VPT 311: General and Systemic Veterinary Pharmacology (2+1)

SYMPATHOMIMETICS

• Adrenaline, isoprenaline and a large number of agents capable of stimulating beta₂ –adrenoceptors are used extensively in the control of bronchial asthma in man.
• Adrenaline has both alpha and beta actions and is more useful in severe anaphylaxis (adrenaline bitartrate 1:1000 solution for injection; large animals 2-4ml, dogs 0.1-0.3 ml intravenously or up to double these doses subcutaneously) while ephedrine and its congeners are used prophylactically in man.
• Direct acting beta₂ agonists are preferred for therapy. Such compounds are exemplified by salbutamol, fenoterol and hexoprenaline. These selective agents are relatively free of dangerous cardiac stimulant side-effects of the formerly used, mixed beta₁ , beta₂ - agonists such as isoprenaline.
• The sympathomimetics are effective in relieving the bronchoconstriction, which follows the release of histamine and /or 5HT from mast cells whose secretory activity they also inhibit.
• Administration as an aerosol reduces the delay to onset of effect to a few minutes. However, aerosol inhalation is not a convenient means of administration for animals. It is recommended in the management of chronic allergies, bronchitis, chronic obstructive pulmonary disease and equine influenza.