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Age Changes By Sue Henderson Pharmacokinetics How body acts on drug: • Reduced renal function, resulting in reduced elimination of renally excreted drugs - toxicity • Dosages should be reduced in the elderly (start low go slow) • Acute illness can lead to rapid decrease in renal function Pharmacokinetics cont… • Lean body mass decreases • Water content of aging body decreases – Volume of hydrophilic drugs decreases • Fat content increases – Distribution of lipophilic drugs increased (eg diazepam) – Implies an increase in half life – Takes longer until a drug effect can be evaluated Pharmacokinetics cont • Absorption of most drugs that permeate gastrointestinal epithelium is not diminished • Transdermal drug absorption may be diminished because of decreased tissue blood perfusion Pharmaco-dynamics • How drugs act on the body • Changes in drug receptors/target organ responses - alter sensitivity to effect of drugs (> CNS effects of benzodiazepines). • Impairment of secondary compensatory mechanisms - predispose to adverse effects (orthostatic hypotension with diuretics or TCAs). Poly-pharmacy • • • • Higher rates of disease in the elderly Take many drugs > interactions/adverse effects Multiple sources (different doctors, hospitals, OTC, friends) • Hoarders of meds. • Medication review to confirm full list of drugs being taken Noncompliance • Unintentional - result confusion, forgetfulness • Intentional - to minimise adverse effects or save money. • People over 65 particularly susceptible to adverse drug reactions(2-3 times higher than <30) • Multimorbidity/high number of medications • Up to one fifth all hospital admissions due to adverse drug effects • Changes in medical status over time can cause long term therapy to become unsafe/ineffective • Advanced age an unpredictable risk factor – elderly may be denied adequate pharmacotherapy • Drug doses used in younger adults may be too high for old individuals • Heterogeneity –no simple rules apply to the entire population – dose needs to be determined individually considering reduction in body weight and renal function • Start from initial smaller dose (say 50%) and titrate to therapeutic effect • Number of drugs administered simultaneously should be reduced as much as possible • Should be reviewed critically and periodically • Adverse drug effects have to be considered when the following symptoms present • Dehydration, postural hypotension, dementia or excitation, confusion, syncope, falls • Especially with diuretics, antihypertensives and psychotropics Minimising adverse effects • • • • • • • whenever possible, use non-pharmacological treatments lowest feasible dose (often less than half usual adult dose) smallest number of medications/simplest dose regimens be familiar drug effects in elderly liquid medications if difficulty in swallowing Simple verbal/written instructions for every medication presenting symptoms may be a result of medications (not old age) • child-proof containers (also elder proof) avoided • Regular review chronic - may be possible to stop medications or reduce dose if renal function declines • Make sure the carer understands treatment References Bochner, F., Rossi, S., Royal Australasian College of General Practitioners, Pharmaceutical Society of Australia, & Australasian Society of Clinical and Experimental Pharmacologists and Toxicologists. (2008). Australian medicines handbook (8th ed.). Adelaide: Australian Medicines Handbook.