C H A P T E R 4 6
Antianginal agents
723
reach peak levels in 60 to 90 minutes and have varying
duration of effects, ranging from 6 to 19 hours. Food
has been found to increase the bioavailability of pro-
pranolol, but this effect has not been found with other
beta-adrenergic blocking agents.
Contraindications and cautions
The beta-blockers are contraindicated in individuals
with bradycardia, heart block and cardiogenic shock
because blocking of the sympathetic response could
exacerbate these diseases.
They are also contraindicated
with pregnancy and breastfeeding
because of the poten-
tial for adverse effects on the fetus or neonate.
Caution should be used in individuals with diabetes,
peripheral vascular disease, asthma, chronic obstructive
pulmonary disease (COPD) or thyrotoxicosis
because
the blockade of the sympathetic response blocks normal
reflexes that are necessary for maintaining homeostasis
in people with these diseases.
Many people with these
complicating disorders receive beta-blockers, and these
individuals need to be monitored carefully to avoid
serious adverse effects.
Adverse effects
Beta-blockers have many adverse effects associated
with the blockade of the sympathetic nervous system.
However, the dose used to prevent angina is lower than
doses used to treat hypertension. Therefore, there is a
decreased incidence of adverse effects associated with
this specific use of beta-blockers.
Adverse effects do occur. CNS effects include
dizziness, fatigue, emotional depression and sleep dis-
turbances. GI problems include gastric pain, nausea,
vomiting, colitis and diarrhoea. Cardiovascular effects
can include heart failure, reduced cardiac output and
arrhythmias. Respiratory effects can include broncho
spasm, dyspnoea and cough. Decreased exercise
tolerance and malaise are also common complaints.
Clinically important drug–drug interactions
A paradoxical hypertension occurs when clonidine is
given with beta-blockers, and an increased rebound
hypertension with clonidine withdrawal may also occur;
it is best to avoid this combination.
A decreased antihypertensive effect occurs when
beta-blockers are given with non-steroidal anti-
inflammatory drugs; if this combination is used, the
person should be monitored closely and a dose adjust-
ment made.
An initial hypertensive episode followed by
bradycardia occurs if these drugs are given with
noradrenaline, and a possibility of peripheral ischaemia
exists if beta-blockers are taken in combination with
ergot alkaloids.
There also is a potential for a change in blood
glucose levels if these drugs are given with insulin or
antidiabetic agents, and the individual will not have the
usual signs and symptoms of hypoglycaemia or hyper-
glycaemia to alert them to potential problems. If this
combination is used, the person should monitor blood
glucose frequently throughout the day and be alert to
new warnings about glucose imbalance.
Prototype summary: Metoprolol
Indications:
Treatment of stable angina pectoris;
also used for treatment of hypertension, prevention
of reinfarction in people with MI, and treatment of
stable, symptomatic HF.
Actions:
Competitively blocks beta-adrenergic
receptors in the heart and kidneys, decreasing
the influence of the sympathetic nervous system
on these tissues and the excitability of the heart;
decreases cardiac output, which results in a
lowered blood pressure and decreased cardiac
workload.
Pharmacokinetics:
Route Onset
Peak
Duration
Oral
15 mins
90 mins
15–19 hours
IV Immediate 60–90 mins 15–19 hours
T
1/2
:
3 to 4 hours; metabolised in the liver and
excreted in urine.
Adverse effects:
Dizziness, vertigo, HF, arrhythmias,
gastric pain, flatulence, diarrhoea, vomiting,
impotence, decreased exercise tolerance.
Care considerations for
people receiving beta-blockers
See Chapter 31 for the care considerations associated
with beta-blockers.
■■
Beta-blockers are used in the treatment of angina to
help restore the balance between supply of oxygen
and demand for oxygen.
■■
Beta-blockers prevent the activation of sympathetic
receptors, which normally would increase heart
rate, increase blood pressure and increase cardiac
contraction. All of these actions would increase the
demand for oxygen; blocking these actions decreases
the demand for oxygen.
KEY POINTS
