Video - Sympathomimetics: Direct agonists

Sympathomimetics are drugs that act on the sympathetic nervous system to produce their effects. They include classes of drugs like alpha agonists and beta-agonists. Both alpha agonists and beta-agonists bind to receptors in the body and activate them.

Alpha agonists activate alpha receptors, which are found primarily in the smooth muscles of the blood vessels and lungs. Alpha agonists are divided into alpha-1 agonists, like phenylephrine and midodrine; and alpha-2 agonists, like clonidine. Phenylephrine is used to treat hypotension, but it can also be used as a decongestant to treat rhinitis, or as a topical agent to cause mydriasis. Midodrine is used to treat orthostatic hypotension; while intravenous and nasal administration of clonidine causes vasoconstriction.

On the other hand, beta-agonists activate beta receptors, which are found in the heart, lungs, and other organs. Beta-agonists are subdivided into non-selective beta agonists like isoproterenol; and selective beta-2 agonists, like albuterol, salmeterol, and terbutaline. Isoprenaline is used to stimulate the heart in individuals with bradycardia or heart block, while albuterol, salmeterol, and terbutaline are used in the treatment of asthma, chronic obstructive pulmonary disease, and hyperkalemia.