C H A P T E R 3 1
Adrenergic blocking antagonists
477
■■
Alpha
1
-selective adrenergic blocking agents decrease
blood pressure by blocking the postsynaptic
alpha
1
-receptor sites, decreasing vascular tone and
promoting vasodilation.
■■
Alpha
1
-selective adrenergic blocking agents are used
to treat hypertension and are often used to treat BPH
because of their relaxing effects on the bladder and
prostate.
NON-SELECTIVE BETA-ADRENERGIC
BLOCKING AGENTS
The
beta-adrenergic blocking agents
(Table 31.4) are
used to treat cardiovascular problems (hypertension,
KEY POINTS
angina, migraine headaches) and to prevent reinfarc-
tion after MI. These drugs are widely used and include
nebivolol (
Nebilet
), oxprenolol (
Corbeton
) (not avail
able in New Zealand), pindolol (
Visken
), propranolol
(
Inderal
), sotalol (
Cardol, Sotacor
) and timolol (
Nyogel
,
Tenopt
). The prototype drug, propranolol, was the first
non-selective beta blocker available.
Therapeutic actions and indications
The therapeutic effects of these drugs are related to
their competitive blocking of the beta-adrenergic recep-
tors in the SNS. The blockade of the beta-receptors in
the heart and in the juxtaglomerular apparatus of the
nephron accounts for the majority of the therapeutic
benefit. Decreased heart rate, contractility and excita-
bility, as well as a membrane-stabilising effect, lead to a
decrease in arrhythmias, a decreased cardiac workload
and decreased oxygen consumption. The juxtaglomer-
ular cells are not stimulated to release renin, which
further decreases the blood pressure. These effects are
useful in treating hypertension and chronic angina and
can help to prevent reinfarction after an MI by decreas-
ing cardiac workload and oxygen consumption. Sotalol
is used exclusively for treating life-threatening ven-
tricular arrhythmias and to maintain sinus rhythm in
individuals with atrial flutter or atrial fibrillation (see
Chapter 45).
Propranolol is very effective in blocking all of the
beta-receptors in the SNS and was one of the first drugs
of the class (see Table 31.4 for usual indications). Since
the introduction of propranolol, newer and more select
ive drugs have become available that are not associated
with some of the adverse effects seen with total blockade
of the SNS beta-receptors. Nebivolol is the newest
adrenergic blocker available and is not associated with
the variety of adverse effects seen with propranolol use.
Oxprenolol blocks autonomic beta-adrenergic receptors
leading to lowering of heart rate and reduces myocardial
demand. Timolol has several recommended uses, which
are listed in Table 31.4; timolol is available in an oph-
thalmic form of the drug for reduction of intraocular
pressure in people with open-angle glaucoma. When
this drug is used topically, eye muscle relaxation occurs.
In addition, because it is applied topically, it is usually
not absorbed systemically from this route.
Pharmacokinetics
These drugs are absorbed from the GI tract after oral
administration and undergo hepatic metabolism. Food
has been found to increase the bioavailability of pro-
pranolol, although this effect was not found with other
beta-adrenergic blocking agents. Absorption of sotalol
is decreased by the presence of food. Propranolol also
crosses the blood–brain barrier, but nadolol and sotalol
do not, making them a better choice if CNS effects
indicate a need to adjust dose or discontinue the
drug if cardiovascular effects are severe.
■
■
Establish safety precautions if CNS effects or
orthostatic hypotension occurs
to prevent injury.
■
■
Arrange for small, frequent meals if GI upset is
severe
to relieve discomfort and maintain nutrition.
■
■
Arrange for supportive care and comfort measures
(rest, environmental control, other measures)
to
decrease CNS effects
; provide headache medication
to alleviate discomfort
; arrange safety measures if
CNS effects occur
to prevent injury.
■
■
Offer support and encouragement
to help the
person deal with the drug regimen.
■
■
Provide thorough teaching, including drug name,
dosage and administration; measures to prevent
adverse effects and warning signs to report to
prescriber; safety measures such as changing
positions slowly and avoiding driving or operating
hazardous machinery, and dietary measures in
conjunction with drug therapy to promote blood
pressure control or alleviate GI upset
to enhance
knowledge about drug therapy and to promote
compliance.
■
■
Offer support and encouragement
to help the
person deal with the drug regimen.
Evaluation
■
■
Monitor response to the drug (lowering of blood
pressure).
■
■
Monitor for adverse effects (GI upset, CNS or
cardiovascular changes).
■
■
Evaluate effectiveness of the teaching plan (person
can name drug, dosage, adverse effects to watch
for and specific measures to avoid them).
■
■
Monitor the effectiveness of comfort measures and
compliance with the regimen.
