Clinical Pharmacology and Therapeutics

CHAPTER 11
DRUGS IN THE ELDERLY
● Introduction 56
● Pharmacokinetic changes 56
● Pharmacodynamic changes 57
● Compliance in the elderly 58
● Effect of drugs on some major organ systems in
the elderly 58
● Practical aspects of prescribing for the elderly 60
● Research 60
INTRODUCTION
The proportion of elderly people in the population is increasing
steadily in economically developed countries. The elderly
are subject to a variety of complaints, many of which are
chronic and incapacitating, and so they receive a great deal of
drug treatment. There is a growing evidence base for the use of
drugs in elderly patients, with important implications for prescribing
of many important classes of drugs, including statins,
β-adrenoceptor antagonists, thrombolytics, ACE inhibitors,
angiotensin receptor blockers, vitamin D and bisphosphonates
(see reviews by Mangoni and Jackson, 2006). Adverse drug
reactions and drug interactions become more common with
increasing age. In one study, 11.8% of patients aged 41–50
years experienced adverse reactions to drugs, but this
increased to 25% in patients over 80 years of age. There are
several reasons for this.
1. Elderly people take more drugs. In one survey in general
practice, 87% of patients over 75 years of age were on
regular drug therapy, with 34% taking three to four
different drugs daily. The most commonly prescribed
drugs were diuretics (34% of patients), analgesics (27%),
tranquillizers and antidepressants (24%), hypnotics (22%)
and digoxin (20%). All of these are associated with a high
incidence of important adverse effects.
2. Drug elimination becomes less efficient with increasing
age, leading to drug accumulation during chronic dosing.
3. Homeostatic mechanisms become less effective with
advancing age, so individuals are less able to compensate
for adverse effects, such as unsteadiness or postural
hypotension.
4. The central nervous system becomes more sensitive to the
actions of sedative drugs.
5. Increasing age produces changes in the immune response
that can cause an increased liability to allergic reactions.
6. Impaired cognition combined with relatively complex
dose regimens may lead to inadvertent overdose.
PHARMACOKINETIC CHANGES
ABSORPTION
Absorption of carbohydrates and of several nutrients, including
iron, calcium and thiamine, is reduced in elderly people.
Lipid-soluble drugs are absorbed by simple diffusion down
the concentration gradient (Chapter 3), and this is not
impaired by age. Intestinal blood flow is reduced by up to 50%
in the elderly. However, age per se does not affect drug
absorption to a large extent (Figure 11.1).
↑Gastric motility
↓Intestinal blood flow
↓Hepatic blood flow
↓Renal blood flow
↓GFR
Metabolism↓
Drug
Figure 11.1: Pharmacokinetic changes with age.
Absorption↔
↓Weight
↓Lean body mass
↑Fat
↓Concentration of
fat-soluble drugs
↑Concentration of
water-soluble drugs
Excretion↓