Geriatric Pharmacology Flashcards
Describe the effect and implications of ageing and co-morbidity on pharmacokinetics and pharmacodynamics Identify key issues in geriatric co-morbidity Explain common adverse drug reactions in the elderly and identify the most common drug-drug and drug-disease interactions
Absorption - alteration with age
Rate of absorption may be delayed
Lower peak concentration
Delayed time to peak concentration being reached
Factors affecting absorption
Route of administration What is taken with drug - food/drugs affecting GI motility and pH Co-morbidity Decreased gastric emptying Dysphagia
Elderly have
Reduced
Increased
Lean body mass
Water
Serum albumin
Kidney weight
Fat as a percentage of body mass
Effect of reduced lean body mass
Reduced VD for drugs which bind to muscle
Effect of reduced body water
Reduced VD for hydrophilic drugs e.g lithium
Effect of reduced plasma protein
albumin
increased % of unbound or free drug e.g diazepam
Effect of increased fat store
Increased VD for lipophilic drugs e.g diazepam
Effect of increased plasma protein
α1-acid glycoprotein
Reduced % unbound drug
Volume of distribution
VD
Effect on metabolism via liver
Causes of change in metabolism
When do most changes occur?
Does not appear to decline equally for all drugs
Decreased blood flow to liver
Decreased liver mass
Decreased ability to heal from injury/malnutrition
Diseases affecting hepatic fx e.g heart failure
Phase 1 reactions involving P450
Stages of metabolism
Phase 1 - modification
- oxidation, reduction, hydrolysis
Phase 2 - conjugation
Phase 1 metabolic stage - and in the elderly?
Phase 2 metabolic stage
Oxidation, reduction and hydrolysis - changes STRUCTURE of molecule
Converts drugs into metabolites to help excretion
Hepatic clearance of drugs metabolised by this is more likely to be prolonged
Adds charged species
Medications are generally preferred in elderly as no accumulation of active metabolites
Elimination of drugs - in elderly?
What happens if it doesn’t occur
Muscle mass loss
Kidney usually - function depleted with age
Prolongation of drugs and potential for accumulation to toxic level
Results in serum creatinine increase - clearance decreased in 2/3
Causes of reduced elimination
Effects
Decreased kidney size
Decreased renal blood flow
Decreased number of functional nephrons
Decreased tubular secretion
Decreased GFR
Decreased drug clearance
Factors affecting drug metabolism
Cardiac index
Maximal breathing capacity
Glomerular filtration
Effects of ageing on pharmacodynamics for
Benzodiazepine
Analgesics
Beta blockers
Anti-cholinergic agents
Increased sensitivity to sedation and psychomotor impairment
Increased level and duration of pain relief
Reduced heart rate response
Increased sensitivity
Factors contributing to adverse drug reaction
Altered organ fx
Decreased homeostatic regulation
Altered drug conc
Multiple drug administration
ADEs
How many are preventable?
When do most errors occur?
Risk factors? 3x
Adverse drug effects
50%
Ordering and monitoring
Polypharmacy
Co-morbidity
Low body weight/BMI
Drug drug interactions
Risk increases with?
Causes
Which drugs are they most common with
Adverse effects ?
e.g benzodiazepine + antidepressant
Number of medications taken
Increased/decreased absorption Additive effects Antagonising effects Changes in metabolism Duplication of drug therapy
CV and psychotropic
Confusing, acute renal failure, cognitive impairment, hypotension
sedation+confusion
Drug-disease interactions
Causes Obesity Ascites dementia Renal/hepatic dysfunction
NSAIDs + hypertension
Alters VD of lipophilic drugs
Alters VD of hydrophilic drugs
Increases sensitivity to CNS or anticholinergic drugs
Impairs metabolism+excretions of drugs
Fluid retention, decreased effect of diuretics
Principles of prescribing for elderly
Start low dose and increase slowly Avoid mixing agents Use one medication for two conditions Consider interactions Adjust doses for renal and hepatic status Avoid prescribing for side effects
Common errors in prescribing for elderly people
Polypharmacy
Missing side effects
Compliance problems
Opening containers
Cognitive impairments
Fear of choking whilst swallowing
Depression
