Alpha2 adrenoceptor agonists in the horse—Areview

In recent years the usefulness of the alpha,, adrenoceptor agonist drugs has been recognized in equine practice. Several agents have become available and are now licensed for use in a number of countries. The principle actions of all alpha₂ adrenoceptor agonists are similar, in that they produce a reduction in heart rate and alteration of heart rhythm, an initial hypertension followed by a prolonged hypotension, a decrease in tile cardiac output and respiratory depression. For clinical purposes, these agents produce sedation and analgesia, they are useful for premedication and markedly potentiate the effects of other sedative/analgesic agents. Differences in receptor specificity between the alpha₂ adrenoceptor agonists results in the distinguishing characteristics of the individual agents, particularly with respect to their duration of action, sedative effect and analgesic properties; their cardiopulmonary effects are however similar, when equipotent sedative closes are administered. When used in combination with other agents, the alpha₂ adrenoceptor agonists all appear to act in a similar manner, with the greatest difference being related to their duration of action.