Adverse drug reactions

Adverse drug reactions - Adverse drug reactions (ADRs) and the effects of drug interactions are discussed on pages 31–35. They may result in symptoms, abnormal physical signs and altered laboratory test results (Box 7.11). ADRs are the cause of around 5% of all hospital admissions but account for up to 20% of admissions in those aged over 65 years. This is partly because older people receive many more prescribed drugs than younger people. Polypharmacy is defined as the use of four or more drugs but may not always be inappropriate, as many conditions such as hypertension and heart failure dictate the use of several drugs, and older people may have several coexisting medical problems. 

Adverse Drug Reactions (ADRs)

Adverse Drug Reactions Second Edition

However, the more drugs that are taken, the greater the risk of an ADR. This risk is compounded by age-related changes in pharmacodynamic and pharmacokinetic factors (pp. 28–29), and by impaired homeostatic mechanisms, such as baroreceptor responses, plasma volume and electrolyte control Older people are thus especially sensitive to drugs that can cause postural hypotension or volume depletion (see Box 7.11). Non-adherence to drug therapy also rises with the number of drugs prescribed.

The clinical presentations of ADRs are diverse, so for any presenting problem in old age the possibility that the patient’s medication is a contributory factor should always be considered. Failure to recognise this may lead to the use of a further drug to treat the problem, making matters worse, where the better course would be to stop or reduce the dose of the offending drug or to find an alternative.

Several factors contribute to polypharmacy (Box 7.12), and it has been shown that most ADRs are preventable. This is achieved by using as few drugs as possible, at the lowest dose possible in easy-to-take formulations, by ensuring that the patient understands the dosage regime, and by reviewing medication regularly. The patient or carer should be asked to bring all medication for review rather than the doctor relying on previous records. Those drugs that are no longer needed or that are contraindicated can then be discontinued.