Adrenergic drugs Adrenergic drugs are also called sympathomimetic drugs because they produce effects similar to those produced by the sympathetic nervous system. Sort by chemical… Adrenergic drugs are classified into two groups based on their chemical

Adrenergic drugs
Adrenergic drugs are also called sympathomimetic drugs because they produce effects
similar to those produced by the sympathetic nervous system.
Sort by chemical…
Adrenergic drugs are classified into two groups based on their chemical structure:
catecholamines (naturally occurring as well as synthetic) and noncatecholamines.
…or by action
Adrenergic drugs are also divided by how they act. They can be:
• direct-acting, in which the drug acts directly on the organ or tissue innervated (suppli
with nerves or nerve impulses) by the sympathetic nervous system
• indirect-acting, in which the drug triggers the release of a neurotransmitter, usually
norepinephrine
• dual-acting, in which the drug has direct and indirect actions. (See How adrenergics
work.)

,Catecholamines
Because of their common basic chemical structure, catecholamines share certain properties—t
stimulate the nervous system, constrict peripheral blood vessels, increase heart rate, and dilate
bronchi. They can be manufactured in the body or in a laboratory. Common catecholamines inc
• dobutamine
• dopamine
• epinephrine, epinephrine bitartrate, and epinephrine hydrochloride
• norepinephrine
• isoproterenol hydrochloride and isoproterenol sulfate.
Pharmacokinetics
Here’s an overview of how catecholamines move through the body.
No P.O.
Catecholamines can’t be taken orally because they’re destroyed by digestive enzymes. In contra
when these drugs are given sublingually (under the tongue), they’re rapidly absorbed through t
mucous membranes. Any sublingual drug not completely absorbed is rapidly metabolized by
swallowed saliva.

,Catecholamines
Subcut vs. IM
Absorption by the subcut route is slowed because catecholamines
cause the blood vessels around the injection site to constrict.
IM absorption is more rapid because less constriction of local blood
vessels occurs.
Catecholamines are widely distributed in the body. They’re
metabolized and inactivated predominantly in the liver but can
also be metabolized in the GI tract, lungs, kidneys, plasma, and
tissues.
On the way out
Catecholamines are excreted primarily in urine; however, a small
amount of isoproterenol is excreted in feces and some epinephrine
is excreted in breast milk.
Memory Tip
To help you remember the effects of catecholamines on alpha and beta
receptors, remember that
A stands for alpha (and activation, suggesting an excitatory response),
and B stands for beta (or banished, which suggests an inhibitory effect).

, Pharmacodynamics of Catecholamines
• Catecholamines are primarily direct-acting. When catecholamines combine with alpha-
adrenergic receptors or beta-adrenergic receptors, they cause either an excitatory or
inhibitory effect. Typically, activation of alpha-adrenergic receptors generates an excitato
response except for intestinal relaxation. Activation of the beta-adrenergic receptors mo
produces an inhibitory response, except in the cells of the heart, where norepinephrine
produces excitatory effects.
Effects on the heart
• The clinical effects of catecholamines depend on the dosage and the route of administrat
Catecholamines are potent inotropes— they make the heart contract more forcefully. As
result, the ventricles of the heart empty more completely with each heartbeat, increasin
the workload of the heart and the amount of oxygen it needs to do this harder work.
Chronotropic effect
• Catecholamines also produce a positive chronotropic effect, which means they cause the
heart to beat faster. That’s because pacemaker cells in the sinoatrial (SA) node of the hea
depolarize at a faster rate. As catecholamines cause blood vessels to constrict and blood
pressure to rise, heart rate can fall as the body tries to compensate and prevent an exces
rise in blood pressure.