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Pharmacodynamics in the older patient

Along side the altered pharmacokinetics in the elderly and of equal importance is the changes in pharmacodynamics that occur due to ageing.

In older people the pharmacodynamic changes that occur relate to alterations both in drug sensitivity and homeostasis - processes by which the internal systems of the body are maintained in balance. Some examples of these changes are:

Drug sensitivity

  • Response to benzodiazepines is increased
  • Response to warfarin is increased
  • b1 and b2 receptor responsiveness is decreased (e.g. response to salbutamol and terbutaline)
  • a2 receptors responsiveness is decreased (e.g. response to clonidine and methyldopa)
  • Response to Opioid analgesics increased.


In older people it is often found that there is an impairment in:

  • Temperature regulation
  • Blood pressure regulation
  • Bladder function
  • Blood sugar levels
  • Fluid and electrolyte balance

Due to the impaired homeostatic mechanisms olderpeople have an increased susceptibility to drug induced side effects such as urinary incontinence, urine retention, confusional states, hypothermia and postural hypotension.


Polypharmacy is the prescribing of multiple drugs for multiple diseases. In the older paient this can lead to problems with drug compliance and is also directly related to the incidence of side effects.

Patients who are over 75 are three times more likely to suffer adverse drug reactions than middle aged adults.

(Greenwall, 2003)

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