308 Prescribing in the elderly

Question 1

What are the 5 common frailty syndromes?

Answer 1

Delirium
Incontinence
Falls
Immobility
Medication side-effects

Question 2

What does ADME stand for?

Answer 2

Absorption
Distribution
Metabolism
Excretion

They’re the things we have to think about when prescribing

Question 3

What factors affect absorption in the elderly?

Answer 3

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

Question 4

Give examples of medications used in the elderly that have specific instruction on use

Answer 4

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

Question 5

What factors affect distribution in the elderly?

Answer 5

Decreased muscle mass
Increased body fat
Decreased serum albumin

Question 6

What are some effects of digoxin toxicity?

Answer 6

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

Question 7

How does decreased muscle mass affect prescribing of digoxin?

Answer 7

↓Lean body mass (muscle)
↓Volume of distribution for drugs that distribute into muscles
= ↑ plasma conc

important for digoxin overdose

Question 8

What drug is increased body fat important for?

Answer 8

Benzodiazepines

↑ body fat
↑ volume of distribution for fat soluble drugs
= ↑ t½

Question 9

What are some side effects of benzodiazepines?

Answer 9

Drowsiness
Confusion
Ataxia
Dependence

Question 10

What is the drug Flumazenil used to treat?

Answer 10

Benzodiazepine overdose

It’s an antagonist with a shorter half life than diazepam and so patient may become re-sedated

Question 11

How does decreased serum albumin affect drug absorption?

Answer 11

↓Albumin 12-25% - further depressed by heart failure, renal disease, rheumatoid arthritis, hepatic cirrhosis some malignancies

Drug binding capacity ↓ 12-25%
↑ free drug

Question 12

What is the drug phenytoin?

Answer 12

A medication for seizures

Question 13

Wat are some signs of phenytoin toxicity?

Answer 13

Nausea, vomiting
Tremor
Ataxia
Nystagmus
Coarse facies
Hepatitis

Question 14

How is albumin concentration relevant to warfarin-aspirin interaction?

Answer 14

-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

Question 15

What are some important drug distribution examples in the elderly?

Answer 15

Decreased muscle mass
-Digoxin

Increased body fat
-Benzodiazepines

Decreased serum albumin
-Warfarin, Phenytoin

Question 16

How is metabolism different in the elderly?

Answer 16

↓ 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

Question 17

How is excretion of drugs different in the elderly?

Answer 17

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

Question 18

What are the signs of lithium toxicity?

Answer 18

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

Question 19

How is morphine metabolised?

Answer 19

Undergoes phase II metabolism by conjugation

Renal impairment results in accumulation of metabolite

Prolonged effect, ↑ toxicity

Question 20

What are the signs of lithium toxicity?

Answer 20

Nausea, vomiting
Constipation
Drowsiness
Respiratory depression
Hypotension

Question 21

How is morphine toxicity treated?

Answer 21

Treatment naloxone iv 400mcg

Question 22

What are some side effects of ACE inhibitors?

Answer 22

Hypotension
Potassium increase
Renal failure
Cough

Question 23

What are some side effects of Ca channel blockers?

Answer 23

Eg. Amlodipine

Hypotension
Negatively inotropic
Fluid retention

Question 24

What are some side effects of diuretics?

Answer 24

Hypotension
Hypokalaemia
Hyponatremia
Confusion
Dehydration