308 Prescribing in the elderly Flashcards
What are the 5 common frailty syndromes?
Delirium
Incontinence
Falls
Immobility
Medication side-effects
What does ADME stand for?
Absorption
Distribution
Metabolism
Excretion
They’re the things we have to think about when prescribing
What factors affect absorption in the elderly?
Reduced saliva
Reduced gastric acid
Decreased GI motility
Reduced surface area for absorption
Reduced splanchnic blood flow
Overall effect:↓ rate of absorption & ↑ time to steady state
Give examples of medications used in the elderly that have specific instruction on use
Levodopa – competes with nutrients
-Plan dosing regimes to avoid meal times
Bisphosphonates
-Advise to take on an empty stomach, sitting up, 30 mins before food
What factors affect distribution in the elderly?
Decreased muscle mass
Increased body fat
Decreased serum albumin
What are some effects of digoxin toxicity?
Cardiac:
heart block, bradycardia, junctional tachycardia
Psychiatric:
delirium, fatigue, malaise, confusion, dizziness
Visual:
blurred or yellow-green vision, halos, double vision, photophobia
GI:
nausea, vomiting, anorexia, diarrhoea, abdominal pain
How does decreased muscle mass affect prescribing of digoxin?
↓Lean body mass (muscle)
↓Volume of distribution for drugs that distribute into muscles
= ↑ plasma conc
important for digoxin overdose
What drug is increased body fat important for?
Benzodiazepines
↑ body fat
↑ volume of distribution for fat soluble drugs
= ↑ t½
What are some side effects of benzodiazepines?
Drowsiness
Confusion
Ataxia
Dependence
What is the drug Flumazenil used to treat?
Benzodiazepine overdose
It’s an antagonist with a shorter half life than diazepam and so patient may become re-sedated
How does decreased serum albumin affect drug absorption?
↓Albumin 12-25% - further depressed by heart failure, renal disease, rheumatoid arthritis, hepatic cirrhosis some malignancies
Drug binding capacity ↓ 12-25%
↑ free drug
What is the drug phenytoin?
A medication for seizures
Wat are some signs of phenytoin toxicity?
Nausea, vomiting
Tremor
Ataxia
Nystagmus
Coarse facies
Hepatitis
How is albumin concentration relevant to warfarin-aspirin interaction?
-Warfarin is highly bound to plasma albumin (99%). It has narrow therapeutic index and a small volume of distribution
Aspirin can displace warfarin from plasma albumin
Displacement of 1-2% of bound warfarin doubles or triples concentration of free warfarin
Outcome: ↑ bleeding
What are some important drug distribution examples in the elderly?
Decreased muscle mass
-Digoxin
Increased body fat
-Benzodiazepines
Decreased serum albumin
-Warfarin, Phenytoin
How is metabolism different in the elderly?
↓ liver volume – up to 30% reduction
↓ liver blood flow 12-40% (extremely variable)
↓ first-pass metabolism due to ↓ blood flow
↓ enzyme activity CP450 (frail elderly)
So smaller doses need to be given because of decreased clearance
How is excretion of drugs different in the elderly?
Renal blood flow
↓ Renal mass (20%)
↓ Renal function (nephrons 30%)
GFR declines by 1% per year from age 40
Drugs that are more than 60% excreted by kidneys are affected by a reduction in renal function
Eg. Lithium and Morphine
What are the signs of lithium toxicity?
Early toxicity Li 1.5 mmol/l
-tremor, agitation, twitching
Intermediate
– lethargy
Late Li >2 mmol/l
-fits, arrhythmia, renal failure – haemodialysis may be needed
How is morphine metabolised?
Undergoes phase II metabolism by conjugation
Renal impairment results in accumulation of metabolite
Prolonged effect, ↑ toxicity
What are the signs of lithium toxicity?
Nausea, vomiting
Constipation
Drowsiness
Respiratory depression
Hypotension
How is morphine toxicity treated?
Treatment naloxone iv 400mcg
What are some side effects of ACE inhibitors?
Hypotension
Potassium increase
Renal failure
Cough
What are some side effects of Ca channel blockers?
Eg. Amlodipine
Hypotension
Negatively inotropic
Fluid retention
What are some side effects of diuretics?
Hypotension
Hypokalaemia
Hyponatremia
Confusion
Dehydration
