C H A P T E R 3 1
Adrenergic blocking antagonists
471
(MI). Table 31.1 shows usual indications for each of
these agents.
Pharmacokinetics
These drugs are well absorbed when given orally and
are distributed throughout the body when given IV or
orally. They are metabolised in the liver and excreted in
faeces and urine. The half-life varies with the particular
drug and preparation.
Contraindications and cautions
The non-selective adrenergic blocking agents are
contraindicated in individuals with known hypersensi-
tivity to any component of the drug
to avoid potentially
serious hypersensitivity reactions
; with bradycardia or
heart blocks,
which could be worsened by the slowed
heart rate and conduction
;
with asthma,
which could
be exacerbated by the loss of noradrenaline’s effect of
bronchodilation
; with shock or heart failure (HF),
which
could become worse with the loss of the sympathetic
BOX 31.1
Drug therapy across the lifespan
Adrenergic blocking agents
CHILDREN
Children are at greater risk for complications associated
with the use of adrenergic blocking agents, including
bradycardia, difficulty breathing and changes in glucose
metabolism.The safety and efficacy for use of these
drugs has not been established for children younger than
18 years of age. If one of these drugs is used, the dose
for these agents needs to be calculated from the child’s
body weight and age. It is good practice to have a second
person check the dose calculation before administering
the drug to avoid potential toxic effects.Two adrenergic
blocking agents have established paediatric doses, and
they might be the drugs to consider when one is needed:
prazosin is used to treat hypertension, and phentolamine,
which is used during surgery for phaeochromocytoma.
Children should be carefully monitored and supported
when these drugs are given.
ADULTS
Adults being treated with adrenergic blocking agents
should be cautioned about the many adverse effects
associated with the drugs. People with diabetes need
to be re-educated about ways to monitor themselves
for hyperglycaemia and hypoglycaemia because the
sympathetic reaction (sweating, feeling tense, increased
heart rate, rapid breathing) usually alerts people that
there is a problem with their glucose levels. People with
severe thyroid disease are also at high risk for serious
adverse effects when taking these drugs, and if one of
them is needed, the person should be monitored very
closely. Propranolol and metoprolol are associated with
more central nervous system (CNS) adverse effects than
other adrenergic blockers, and people who have CNS
complications already or who develop CNS problems
while taking an adrenergic blocker might do better with
a different agent.
PREGNANCY AND BREASTFEEDING
In general, there are no adequate studies about the effects
of adrenergic blockers during pregnancy and breastfeeding,
and they should be used only in those situations in which
the benefit to the mother is greater than the risk to the
fetus or neonate. Adrenergic blockers can affect labour,
and babies born to mothers taking these drugs may exhibit
adverse cardiovascular, respiratory and CNS effects.
Many of these drugs were teratogenic in animal studies.
Because of a similar risk of adverse reactions on the baby,
breastfeeding mothers should find another way to feed the
baby if an adrenergic blocking drug is needed.
OLDER ADULTS
Older people are more likely to experience the adverse
effects associated with these drugs—CNS, cardiovascular,
GI and respiratory effects. Because older people often
also have renal or hepatic impairment, they are more
likely to have toxic levels of the drug related to changes
in metabolism and excretion.The older person should
be started on lower doses of the drugs and should be
monitored very closely for potentially serious arrhythmias
or blood pressure changes. Bisoprolol is often a drug of
choice for older people who require an adrenergic blocker
for hypertension because it is not associated with as many
problems in the elderly and regular dosing profiles can
be used.
People who use alternative therapies as part of their
daily regimen should be cautioned about potential
increased adrenergic blocking effects if the following
alternative therapies are combined with adrenergic
blocking agents:
• Ginseng, sage—increased antihypertensive effects (risk
of hypotension and increased CNS effects)
• Xuan shen, nightshade—slow heart rate (risk of severe
bradycardia and reflex arrhythmias)
• Celery, coriander, Di huang, fenugreek, goldenseal,
Java plum, xuan seng—lower blood glucose (increased
risk of severe hypoglycaemia)
• Saw palmetto—increased urinary tract complications
People who are prescribed an adrenergic blocking
drug should be cautioned about the use of herbs, teas
and alternative medicines. If a person feels that one of
these agents is needed, the healthcare provider should
be consulted and appropriate precautions should be
taken to ensure that the person is able to achieve the
most therapeutic effects with the least adverse effects
while taking the drug.
Herbal and alternative therapies
BOX 31.2
