McKenna's Pharmacology for Nursing, 2e - page 497

C H A P T E R 3 1 Adrenergic blocking antagonists 485
CHAPTER SUMMARY
■■Adrenergic blocking agents, or sympatholytic drugs,
lyse, or block, the effects of the sympathetic nervous
system (SNS).
■■Both the therapeutic and the adverse effects
associated with these drugs are related to their
blocking of the normal responses of the SNS.
■■The alpha- and beta-adrenergic blocking agents block
all of the receptor sites within the SNS, which results
in lower blood pressure, slower pulse and increased
renal perfusion with decreased renin levels. These
drugs are indicated for the treatment of essential
hypertension. They are associated with many adverse
effects, including lack of bronchodilation, cardiac
suppression and diabetic reactions.
■■Selective adrenergic blocking agents have been
developed that, at therapeutic levels, have specific
affinity for alpha- or beta-receptors or for specific
alpha1-, beta1-, or beta2 - receptor sites. This
specificity is lost at levels higher than the therapeutic
range.
■■Alpha-adrenergic drugs specifically block the alpha-
receptors of the SNS. At therapeutic levels, they do
not block beta-receptors.
■■Non-specific alpha-adrenergic blocking agents are
used to treat phaeochromocytoma, a tumour of the
adrenal medulla.
■■Alpha 1-selective adrenergic blocking agents block the
postsynaptic alpha1-receptor sites, causing a decrease
in vascular tone and a vasodilation that leads to a fall
in blood pressure without the reflex tachycardia that
occurs when the presynaptic alpha 2 -receptor sites are
also blocked.
■■Beta-blockers are drugs used to block the beta-
receptors within the SNS. These drugs are used for
a wide range of conditions, including hypertension,
stage fright, migraines, angina and essential tremors.
■■Blockade of all beta-receptors results in a loss of the
reflex bronchodilation that occurs with sympathetic
stimulation. This limits the use of these drugs in
individuals who smoke or have allergic or seasonal
rhinitis, asthma or COPD.
■■Beta1-selective adrenergic blocking agents do not
block the beta2 -receptors that are responsible for
bronchodilation and therefore are preferred in people
with respiratory problems.
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ONLINE RESOURCES
An extensive range of additional resources to enhance teaching
and learning and to facilitate understanding of this chapter may
be found online at the text’s accompanying website, located on
thePoint athttp://thepoint.lww.com.These include Watch and
Learn videos, Concepts in Action animations, journal articles,
review questions, case studies, discussion topics and quizzes.
WEB LINKS
Healthcare providers and students may want to consult
the following Internet sources:
www.heartfoundation.org.au
Home page of the Heart Foundation Australia.
Information, support groups, diet, exercise and
research information on hypertension and other
cardiovascular diseases.
www.heartfoundation.org.nz
Home page of the National Heart Foundation New
Zealand. Information, support groups, diet, exercise
and research information on hypertension and other
cardiovascular diseases.
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