1. Age Changes
By Sue Henderson

2. 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

3. 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
Volume distribution of hydrophilic drugs (aspirin, lithium, alcohol) reduced (equal doses as in younger individuals will result in higher plasma concentrations - toxic)
Distribution of lipophilic (diazepam) drugs is increased

4. 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

5. 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).

6. 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

7. Noncompliance Unintentional - result confusion, forgetfulness
Intentional - to minimise adverse effects or save money.

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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.