Pharmacodynamics
Goals of Prescribing
General risk factors for falling in the elderly:
- Conditions that affect mobility or balance (such as arthritis, stroke, Parkinson's disease, arrhythmias, heart failure)
- Frailty (for example physical disability, general weakness).
Drug treatments:
- Drugs that can cause postural hypotension, sedation, tachycardia or periods of asystole.
- Psychoactive drugs (such as benzodiazepines, antidepressants).
Orthostatic responses and postural control
- Blunting of reflex tachycardia - increased risk of hypotension arising from medication e.g antihypertensives, benzodiazepines, antiparkinsonian drugs
Cognitive function
- Reduced cholinergic transmission - increased risk of confusion arising from medication e.g hypnotics, antichloinergics, b-blockers
Visceral muscle function
- Reduced bowel motililty - increased risk of constipation arsing from opiates, antihistamines, anticholinergics
- Bladder instability - urinary retention and incontinence
- Avoid polypharmacy and unnecessary drug therapy
- Treat the CAUSE rather than the symptom (may be an ADR from a current medicine)
- Take into account all co-morbidities
- Elderly patients may need reduced doses and smaller dose titrations.
- ADRs occur more frequently
- Ensure compliance - BP's, counselling
Pharmacokinetics
1. Absorption
- Reduced gastric acid secretion and gastric motility
2. Distribution
- Reduced total body water
- Increased total body fat
- Reduced serum albumin
3. Metabolism
- Reduced hepatic mass and hepatic blood flow
4. Excretion
- Generally GFR declines (as well as renal blood flow and renal tubular function)
Scenario
Contents
An 80 year-old woman presented to an outpatient clinic with a history of severe blackouts.
Past medical history: angina and HTN
DHx: bendroflumethiazide 2.5mg od
isosorbide mononitrate 60mg od
Her GP had recently commenced nifedipine SR 20mg bd for poorly controlled HTN. On examination her BP was 120/70mmHg while supine and 90/60mmHg on standing.
What are the underlying problems in this patient? what would you advise?
Introduction
- Introduction
- Pharmacokinetics
- Pharmacodynamics
- Falls risk
- Goals of prescribing
- Scenario
- References
The proportion of older people in our society is growing.
People over 65 account for the highest activity and spend across primary, secondary and social care.
As a result of ageing, physiological changes can effect the pharmacokinetic and pharmacodynamic properties of drugs.
Walker, R, Whittlesea, C. Clinical pharmacy and therapeutics 4th edition 2007, Geriatrics 135
Falls - risk assessment, National Institute of Clinical Excellence http://cks.nice.org.uk/falls-risk-assessment#!scenariorecommendation
National service framework for older people - http://www.nhs.uk/nhsengland/NSF/pages/Olderpeople.aspx
Principles of Prescribing in the Elderly