Noncatecholamines
Noncatecholamine
adrenergic drugs have a variety of therapeuticuses because of the many effects they can
have on the body, in-cluding:
·
local or systemic constriction of blood vessels (phenylephrine)
·
nasal and eye decongestion and dilation of the bronchioles (al-buterol,
bitolterol, ephedrine, formoterol, isoetharine hydrochlo-ride, isoproterenol,
levalbuterol, metaproterenol, pirbuterol, sal-meterol, and terbutaline)
·
smooth-muscle relaxation (terbutaline).
Although these drugs are all excreted in urine,
they’re absorbed in different ways.
Absorption of the noncatecholamines depends on the
administra-tion route:
·
Inhaled drugs, such as albuterol, are absorbed gradually from the
bronchi and result in lower drug levels in the body.
·
Oral drugs are absorbed well from the GI tract and are distrib-uted widely
in body fluids and tissues.
·
Some noncatecholamines, such as ephedrine, cross the blood-brain barrier
and can be found in high concentrations in the brain and cerebrospinal fluid
(fluid that moves through and protects the brain and spinal canal).
Noncatecholamines are metabolized and inactivated
primarily in the liver but also in the lungs, GI tract, and other tissues.
Noncatecholamines and their metabolites are
excreted primarily in urine. Some, such as inhaled albuterol, are excreted
within 24 hours; others, such as oral albuterol, within 3 days. Acidic urine
increases excretion of many noncatecholamines; alkaline urine slows excretion.
Noncatecholamines can be direct-acting,
indirect-acting, or dual-acting (unlike catecholamines, which are primarily
direct-acting).
·
Direct-acting noncatecholamines that stimulate alpha receptors include
phenylephrine. Those that selectively stimulate beta2 re-ceptors include albuterol, isoetharine,
metaproterenol, and terbu-taline.
·
Dual-acting noncatecholamines include ephedrine.
Noncatecholamines stimulate the sympathetic nervous
system, producing a variety of effects in the body. Phenylephrine, for
ex-ample, causes vasoconstriction and is used to treat hypotension in cases of
severe shock. Terbutaline is used to stop preterm labor.
Here are a few examples of drugs that interact with
noncatechol-amines:
·
Anesthetics (general), cyclopropane, and halogenated hydrocar-bons can
cause arrhythmias. Hypotension can also occur if these drugs are taken with
noncatecholamines that exert predominantly beta2 activity, such as terbutaline.
·
Monoamine oxidase inhibitors can cause severe hypertension and even
death.
·
Oxytocic drugs that stimulate the uterus to contract can be in-hibited
when taken with terbutaline. When taken with other non-catecholamines, oxytocic
drugs can cause hypertensive crisis or a stroke.
·
Tricyclic antidepressants can cause hypertension and arrhyth-mias.
·
Urine alkalizers, such as acetazolamide and sodium bicarbon-ate, slow
excretion of noncatecholamines, prolonging their dura-tion of action. (See Adverse reactions to noncatecholamines.)
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