A-Textbook-of-Clinical-Pharmacology-and-Therapeutics-5th-edition

58 DRUGS IN THE ELDERLY
antagonists, tricyclic antidepressants and diuretics is increased
in elderly patients. The QT interval is longer in the elderly,
which may predispose to drug-induced ventricular tachydysrhythmias.
Clotting factor synthesis by the liver is reduced
in the elderly, and old people often require lower warfarin
doses for effective anticoagulation than younger adults.
Key points
Pharmacodynamic changes in the elderly include:
• increased sensitivity to central nervous system (CNS)
effects (e.g. benzodiazepines, cimetidine);
• increased incidence of postural hypotension (e.g.
phenothiazines, beta-blockers, tricyclic antidepressants,
diuretics);
• reduced clotting factor synthesis, reduced warfarin for
anticoagulation;
• increased toxicity from NSAIDs;
• increased incidence of allergic reactions to drugs.
COMPLIANCE IN THE ELDERLY
Incomplete compliance is extremely common in elderly people.
This is commonly due to a failure of memory or to not understanding
how the drug should be taken. In addition, many
patients store previously prescribed drugs in the medicine
cupboard which they take from time to time. It is therefore
essential that the drug regimen is kept as simple as possible
and explained carefully. There is scope for improved methods
of packaging to reduce over- or under-dosage. Multiple drug
regimens are confusing and increase the risk of adverse interactions
(see Chapter 13).
EFFECT OF DRUGS ON SOME MAJOR
ORGAN SYSTEMS IN THE ELDERLY
CENTRAL NERVOUS SYSTEM
Cerebral function in old people is easily disturbed, resulting
in disorientation and confusion. Drugs are one of the factors
that contribute to this state; sedatives and hypnotics can easily
precipitate a loss of awareness and clouding of consciousness.
NIGHT SEDATION
The elderly do not sleep as well as the young. They sleep for a
shorter time, their sleep is more likely to be broken and they are
more easily aroused. This is quite normal, and old people should
not have the expectations of the young as far as sleep is concerned.
Before hypnotics are commenced, other possible factors
should be considered and treated if possible. These include:
1. pain, which may be due to such causes as arthritis;
2. constipation – the discomfort of a loaded rectum;
3. urinary frequency;
4. depression;
5. anxiety;
6. left ventricular failure;
7. dementia;
8. nocturnal xanthine alkaloids, e.g. caffeine in tea,
theophylline.
A little more exercise may help, and ‘catnapping’ in the day
reduced to a minimum and regularized (as in Mediterranen
cultures).
The prescription of hypnotics (see Chapter 18) should be
minimized and restricted to short-term use.
ANTIDEPRESSANTS
Although depression is common in old age and may indeed
need drug treatment, this is not without risk. Tricyclic antidepressants
(see Chapter 20) can cause constipation, urinary
retention and glaucoma (due to their muscarinic blocking
action which is less marked in the case of lofepramine than
other drugs of this class), and also drowsiness, confusion, postural
hypotension and cardiac dysrhythmias. Tricyclic antidepressants
can produce worthwhile remissions of depression
but should be started at very low dosage.
Selective 5-hydroxytryptamine reuptake inhibitors (e.g.
fluoxetine) are as effective as the tricyclics and have a distinct
side-effect profile (see chapter 20). They are generally well
tolerated by the elderly, although hyponatraemia has been
reported more frequently than with other antidepressants.
ANTI-PARKINSONIAN DRUGS
The anticholinergic group of anti-parkinsonian drugs (e.g.
trihexyphenidyl, orphenadrine) commonly cause side effects
in the elderly. Urinary retention is common in men. Glaucoma
may be precipitated or aggravated and confusion may occur
with quite small doses. Levodopa combined with a peripheral
dopa decarboxylase inhibitor such as carbidopa can be effective,
but it is particularly important to start with a small dose,
which can be increased gradually as needed. In patients with
dementia, the use of antimuscarinics, levodopa or amantidine
may produce adverse cerebral stimulation and/or hallucinations,
leading to decompensation of cerebral functioning,
with excitement and inability to cope.
CARDIOVASCULAR SYSTEM
HYPERTENSION
There is excellent evidence that treating hypertension in the
elderly reduces both morbidity and mortality. The agents used
(starting with a C or D drug) are described in Chapter 28. It is
important to start with a low dose and monitor carefully.
Some adverse effects (e.g. hyponatraemia from diuretics) are
much more common in the elderly, who are also much more
likely to suffer severe consequences, such as falls/fractures
from common effects like postural hypotension. Alphablockers
in particular should be used as little as possible.
Methyldopa might be expected to be problematic in this age
group but was in fact surprisingly well tolerated when used as
add-on therapy in a trial by the European Working Party on
Hypertension in the Elderly (EWPHE).