Prescribing in the Elderly

Question 1

what are the 4 principles of pharmacokinetics?

Answer 1

ADME
absorption
distribution
metabolism
excretion

Question 2

what are the 2 principles of absorption?

Answer 2

acidic drugs require an acidic environment for absorption (phenytoin, aspirin, penicillin)
basic drugs require basic environment for absorption (diazepam, morphine, pethidine)

Question 3

how is drug absorption different in elderly?

Answer 3

less stomach acid so stomach is more basic
basic drugs are therefore more absorbed in elderly than in younger people
decreased small bowel surface area

Question 4

what are the principles of distribution?

Answer 4

protein binding (free vs bound proportion of drugs)
- albumin (basic) binds to acidic drugs
- alpha 1 acid glycoprotein (acidic) binds to basic drugs
lipid binding
- increases the volume of distribution of lipophilic drugs

Question 5

how is distribution different in the elderly?

Answer 5

elderly generally have low albumin but a higher A-1 AG, therefore better distribution of basic drugs
increased fat (proportional to muscle mass), therefore lipophilic drugs are better distributed

Question 6

what can the volume of distribution tell you about a drug?

Answer 6

higher volume of distribution = higher lipid solubility = longer half life

Question 7

how is volume of distribution calculated?

Answer 7

//

Question 8

what is volume of distribution?

Answer 8

the theoretical volume necessary to contain all of the administered drug if it was at the concentration observed in the blood plasma

Question 9

how can weight loss affect drug action?

Answer 9

loss of fat = Vd reduced = higher concentration of drug in plasma = side effects (delirium etc)

Question 10

how does clearance affect half life of a drug?

Answer 10

lower clearance rate = longer half life

Question 11

how is hepatic metabolism different in the elderly?

Answer 11

reduced liver function due to decreased size and blood flow and disease
reduced first pass metabolism
reduced levels of bio-transforming enzymes
reduces clearance and can cause increased half life/action of the drug

Question 12

how is renal metabolism different in the elderly?

Answer 12

lower GFR (due to decreased size, tubular secretion and renal blood flow)

Question 13

general principle of pharmacodynamics in the elderly?

Answer 13

lower doses have same effect in the elderly but some effects are decreased (B Blockers don’t have as much of a bradykinic affect)

Question 14

how is the therapeutic index calculated?

Answer 14

50% lethal dose / 50% effective dose
or
minimum toxic dose / minimum effective dose
if both values are similar will give a small therapeutic index

Question 15

give examples of drugs with a small therapeutic index?

Answer 15

theophylline
warfarin
lithium
digoxin
gentamicin
vancomycin

Question 16

how does therapeutic window change with age?

Answer 16

gets narrower
therapeutic response reduces
toxic response increases

Question 17

name 4 drugs associated with adverse effects in elderly?

Answer 17

warfarin
digoxin
insulin
benzodiazepines

Question 18

name 6 drugs with side effects in elderly?

Answer 18

opioids = constipation
- also give lactulose/senna prophylaxis
steroids = osteoporosis, diabetes
levothyroxine
- calcium interferes with levothyroxine absorption - stop calcium tablets
NSAIDs = GI bleed, reduced GFR, decreased effect of diuretics/anti-hypertensives
- swap to paracetamol
benzodiazepines = impaired cognitive function
antibiotics = resistance, C. Diff

Question 19

what is Beers criteria?

Answer 19

3 categories of drugs

• always avoided
• potentially bad
• used with caution

Question 20

principles of polypharmacy?

Answer 20

review medications regularly
avoid treating side effects with more drugs - reduce dose or swap drug instead
try and prescribe one drug that helps more than one problem
if stable, use combination preparation

Question 21

what is the STOPP-START tool?

Answer 21

list of drugs in 2 categories used for prescribing in elderly
STOPP = Screening Tool of Older People’s Potentially inappropriate Prescriptions
START = Screening Toll to Alert Doctors to Right Treatments

Question 22

STOPP GI drugs?

Answer 22

loperamide/codeine phosphate in certain circumstances
metoclopramide in people with parkinsons
stimulant laxatives in people with bowel obstruction

Question 23

START GI drugs?

Answer 23

PPI for reflux, stricture or patients >80 on anti-platelets and SSRIs
fibre supplement

Question 24

STOPP cardio drugs?

Answer 24

beta blockers if taking verapamil
non-selective beta blocker in COPD patients
CCBs in chronic constipation or taking diltiazem/verapamil with heart failure
dipyridamole as monotherapy
statins

Question 25

START cardio drugs?

Answer 25

antihypertensives
ACE inhibitor (chronic heart failure or post MI)
PPI (with aspirin + warfarin)
warfarin/DOACs (chronic AF)

Question 26

how is adherence in elderly?

Answer 26

generally the same as younger people