geriatric pharmocology Flashcards
What are challenges?
New drugs each year
Polypharmacy
Med costs
Advanced understanding of interactions
Med compliance
How does ageing affect absorption?
Rate may be delayed
Lower peak conc
Delayed time to peak conc
What factors affect absorption?
Route
What is taken w the drug
Comorbidity
Increased GI pH
Decreased gastric emptying
Dysphagia
What does the body of an older person look like?
Reduced lean body mass, body water, serum albumin, kidney weight
Increased fat as a % body mass
How does ageing affect volume of distribution?
Reduced VD for drugs that bind to muscle (digoxin)
Reduced VS for hydrophilic drugs (ethanol, lithium)
Reduced % unbound/free drug (propanalol, amitriptyline)
Increased % of unbound/free drug (diazepam, warfarin)
Increased VD for lipophilic drugs (diazepam)
What is metabolism?
Phase I- modification
Converts drugs into metabolites
Hepatic clearance of drugs via phase I prolonged in elderly
Phase II- conjugation
Adds charged species
Preferred in elderly due to inactive metabolites
Liver- decreased blood flow, mass
-decline of ability to recover from injury
-malnutrition
-diseases affecting hepatic
How does ageing affect elimination?
Creatinine clearance decrease
Decreased GFR and drug clearance
Prolongation of drugs half life
Possibility of accumulation to toxic level of dose not modified
Decreased kidney size, blood flow, no of functional nephrons, tubular secretion
What are some effects of ageing on pharmacodynamics?
Benzodiazepine- increased sensitivity to sedation and psychomotor impairment
Analgesic- increased level and duration of relief
Beta blockers- decreased HR response
Anticholinergic agents- increased sensitivity
What are risk factors for Adverse Drug Events?
Polypharmacy
Comorbidity
Low body weight or BMI
What are causes of drug interactions?
In/decrease drug absorption
Additive effects due to similar effects
Antagonising effects to opposite effects
Changes in metabolism
Duplication of drug therapy
Obesity (lipophilic drugs), ascites (hydrophilic drugs), dementia (paradoxical reaction), renal/hepatic dysfunction (metabolism)
What are adverse effects of drug interactions?
Confusion
Cognitive impairment
Hypotension
Acute renal failure
What are some drug interactions?
NSAIDs and congestive HF (fluid retention)
Alpha blockers and anticholinergics (urinary retention)
NSAIDs and gastropathy (increased ulcer/bleeding risk)
NSAIDs and hypertension (fluid retention)
What are principles of prescribing in the elderly?
Start w low dose and titration slowly
Avoid starting 2 at same time
Reach therapeutic dose before changing
Avoid prescribing to tx side effects
Use 1 med to tx 2 conditions
Consider drug interactions
Use simplest regime
Avoid therapeutic duplication
Determine endpoints and plan for assess
Adjust doses for renal and hepatic impairment
Why might the elderly not adhere?
Financial
Congnitive
Functional
Beliefs/understanding
Opening containers
Concerns after reading labels
Depression
What are common errors in prescribing?
Polypharmacy
Side effects missed (part of ageing misinterpretation)
Different doctors
Doctors assume pt not taking meds but instead were prescribed too much
