Geriatric Pharmacology Flashcards
What are the challenges of geriatric pharmacology?
New drugs Changing managed-care formularies Understanding of drug-drug interactions Co-morbid states Polypharmacy Medication compliance Effects of ageing physiology on drug therapy Medication cost
What are the effects of ageing on absorption of drugs?
- Rate delayed
- Lower peak concentration
- Delayed time to peak concentration
BUT slow GI tract gives time for absorption
What factors affect absorption?
Route of administration What is taken with the drug: food, drugs that influence gastric pH and drugs that promote or delay GI motility Comorbidity Increased GI pH Decreased gastric emptying Dysphagia
What reduces with age?
Lean body mass
Body water
Serum albumin (binds to many drugs)
Kidney weight
What increases with age?
Fat as a percentage of body mass
How does a reduced lean body mass effect VD (volume distribution)?
Reduced VD for drugs that bind to muscle (digoxin)
How does a reduced body water effect VD?
Reduced VD for hydrophilic drugs (ethanol and lithium)
How does reduced plasma protein (albumin) effect VD?
Increased percentage of unbound or free drug (active) (diazepam, warfarin)
How does an increased fat store effect VD?
Increased VD for lipophilic drugs (diazepam, trazadone)
How does an increased plasma protein effect volume of distribution (VD)?
Reduced % unbound or free drug (active) (propanolol)
When does capacity of the liver to metabolise drugs change?
Most changes occur in phase 1 reaction (P450)
What causes a change in liver capacity to metabolise drugs?
Decreased bloodflow in liver
Decreased liver mass
Decline of liver’s ability to recover from injury malnutrition
Diseases affecting hepatic functions (e..g heart failure)
What are the phases of drug metabolism?
Phase 1: modification (oxidation, reduction, hydrolysis)
- Converts drugs into metabolites to facilitate excretion
- Hepatic clearance of drugs metabolised by phase 1 rxns is more likely to be prolonged in the elderly
Phase II: Conjugation:
- Adds charged species (Sulphate, glycine)
- Meds undergoing phase II hepatic metabolisms are generally preferred in the elderly due to inactive metabolites (no accumulation)
What impacts drugs ability to be eliminated?
Age related decrease of kidney function
Impacts of reduced drug elimination?
More drug stays in system = takes more time for drug to be eliminated (drug prolongation)
= Accumulation to toxic level if dosage is not modified
What else reduces drug elimination?
Decreased kidney size
Decreased renal bloodflow
Decreased number of functional nephrons
Decreased tubular secretion
Results of reduced drug elimination?
Decreased glomerular filtration rate
Decreased drug clearance
What impact does a reduced cardiac index have on the body?
Bloodflow to organs decreased = clearance reduced
What impact does a reduced maximal breathing capacity have on drugs?
Affects clearance of inhaled anaesthetics
Impacts on benzodiazepine?
Increase sensitivity to sedation and psychomotor impairment
Impacts on analgesics?
Increased level and duration of pain relief
Impacts on beta-blockers?
Decreases HR response
Impacts on anti-cholinergic agents?
Increased sensitivity
What causes adverse drug rxns in elderly pts?
Impaired organ func = multiple disease states = multiple drug administration = altered compliance = adverse drug rxn
Impaired organ func = Altered organ func = adverse drug rxn
Altered drug concentration or decreased homeostatic regulation = adverse drug rxn
When do most adverse drug events occur?
At the ordering and monitoring stages
50% are considered preventable
Risk factors of adverse drug events?
Polypharmacy
Co-morbidity
Low body weight or body mass index
What causes drug-drug interactions?
Increased or decreased drug’s absorption
Additive effects due to similar effects of drugs
Antagonising effects due to opposite effects of drugs
Changes in drug metabolism
Duplication of drug therapy
Where are most drug-drug interactions seen?
CV and psychotic drugs
What can adverse effects cause?
Confusion
Cognitive impairment
Hypotension
Acute renal failure
What is the risk of the combination: benzodiazepine + antidepressant + antipsychotic?
Sedation, confusion
Causes of drug-disease interactions?
Obesity alters volume of distribution of lipophilic drugs
Ascites alters VD of hydrophilic drugs
Dementia can increase sensitivity to drugs with CNS or anticholinergic activity
Renal or hepatic dysfunction may impair metabolism and excretions of drugs
Risks of combining NSAIDs and hypertension?
Fluid retention - decreased effectiveness of diuretics
Principles of prescribing in the elderly?
Non-adherence
Start with a low dose and titrate slowly
Avoid starting 2 agents at same time
Reach therapeutic dose before switching or adding agents
Determine therapeutic endpoints and plan for assessment
Avoid prescribing to treat side effect of another drug
Use 1 med to treat 2 conditions
Consider drug-drug and drug-disease interactions
Adjust doses for renal and hepatic impairment
What factors to consider regarding prescribing drugs to the elderly?
Financial
Cognitive
Functional status
Beliefs and understanding about disease and medications
Common errors in prescribing for the elderly?
Polypharmacy - a drug for every complaint
Side effects missed as thought to be part of ageing
Elderly see different doctors
Physicians often think pts are ill as not taking meds but they’re taking them too much
Why is compliance a problem for taking medications?
Opening containers (weak, arthritis, tremors)
Cognitive impairment
Fear of choking or concerns after reading info
Depression - tired = poor time concept for doses
Adverse drug rxns limit benefit of meds
