Veterinary Neuropharmacology

THERAPEUTIC USES

• Acute anaphylactic reaction – to counter hypotension (α) and bronchospasm (β), epinephrine is the drug of choice.
• Allergic disorders, asthma – Objective is to produce brnchodilatation via β₂ receptors.  Isoproterenol or epinephrine can be used by inhalation or by intramuscular or intravenous injection. They are short acting and also produce marked cardiac stimulation via the β1 receptors. Ephedrine can also be used. Though it is long acting, it produces marked CNS stimulation.
• Cardiac arrest/heart block – intracardiac injections of epinephrine or isoproterenol followed by IV infusion or subcutaneous and intramuscular injections are useful.
• In combination with local anaesthetics – to produce local vasoconstriction and retard the removal of the anaesthetic thereby, increasing the duration of anaesthetic action. Epinephrine is preferred for this use.
• Control of bleeding – epinephrine when applied locally arrests bleeding from arterioles and capillaries.
• Decongestion of mucous membrane – phenylephrine and pseudoephedrine are used in rhinitis, sinusitis and hay fever as decongestant.
• Ophthalmology – ephedrine or phenylephrine can be used to examine the eye as they induce mydriasis without cyclopegia.
• Shock – Use of α agonists to maintain blood pressure in shock may be harmful by reducing the perfusion to the kidney and brain, which are already affected. But dopamine is useful in the treatment of cardiogenic, traumatic and hypovolemic shock because it selectively dilates the kidney blood vessels, increasing glomerular filtration and increasing urine production. In addition dopamine increases blood supply to abdominal organs.
• Hypertension – clonidine is effective in hypertension and its effect is primarily central. It may partially activate peripheral presynaptic α₂ receptors.
• Uterine relaxants – isoxuprine can be used to produce uterine relaxation (tocolytic).