Once a diagnosis has been made and medical treatment is deemed necessary, safe and effective pharmacologic agents that exert
the appropriate actions should be selected. Factors to be
considered include dose and frequency of administration of the chosen drugs, the optimal routes for delivery, the particular pharmaceutical forms to be used, any public health or environmental implications, and regulatory constraints. For selected therapies, such as antimicrobials, distribution to the site of action also should be considered. Although the Animal Drug Medicinal Use Act of 1994 legalizes extra-label drug use in the USA, selected states or other countries may have additional or complementary regulatory or legal restrictions. In all instances, it is important to read carefully the label instructions for use of specific drugs.Positive inotropes increase the strength of cardiac muscle contraction by increasing the quantity of
intracellular calcium available for binding by muscle proteins. This, in turn, augments contractile protein interaction in the myocardial cell. Intracellular calcium can be increased by altering the Na+/Ca2+ exchange pump, by increasing production of cyclic adenosine monophosphate (cAMP) via stimulation of adenylate cyclase, or by decreasing degradation of cAMP via inhibition of phosphodiesterases. A new class of inotropic agents increases the sensitivity of contractile protein to calcium.