5. Polypharmacy and drug-drug interactions

Question 1

Why is polypharmacy and drug interactions important?

Answer 1

-causes distress to patient/ families
-may disrupt stable conditions
-potentially fatal

Question 2

Define polypharmacy

Answer 2

Prescribing of multiple items to one individual

Question 3

What is health inequality?

Answer 3

individuals living in the most deprived communities more likely to experience polypharmacy

Question 4

Why are older people likely to experience polypharmacy?

Answer 4

-treated for multiple conditions
-altered pharmacokinetics and pharmacodynamics
-use of OTC and herbals

Question 5

Why are patients with long term conditions/ co-morbidities?

Answer 5

-multiple disease states and multiple drugs combine to cause interactions and ADRs
-Altered pharmacokinetics

Question 6

People with learning disabilities?

Answer 6

-potentially treated for multiple conditions
-inappropriate use for antipsychotic medications

Question 7

What are examples of appropriate polypharmacy?

Answer 7

-manage conditions effectively
-primary or secondary prevention
-avoid tablet burden
-improves concordance

Question 8

What are examples of problematic polypharmacy?

Answer 8

-tablet burden
-drug-drug interactions
-adverse drug reactions
-poor concordance

Question 9

What are behavioural drug-drug interactions?

Answer 9

occur when one drug alters the patient’s behaviour to modify compliance with another drug

Question 10

What are pharmaceutic drug-drug interactions?

Answer 10

occur when the formulation of one drug is altered by another before it is administrated

Question 11

What are pharmacokinetic drug-drug interactions?

Answer 11

when now drug changes the systemic concentration of another drug, altering ‘how much’ and for ‘how long’ it is present at the site of action

Question 12

What are pharmacodynamic drug-drug interactions?

Answer 12

when interacting drugs have either additive effects, in which case the overall effect is increased or opposing effects in which case the overall effect is decreased or ‘cancelled out’

Question 13

Explain how polypharmacy patients more susceptible to drug interactions?

Answer 13

-multiple disease states and multiple drugs combine to cause interactions and ADRs

Question 14

Explain how elderly patients more susceptible to drug interactions?

Answer 14

-usually have polypharmacy, also altered pharmacokinetics and pharmacodynamics

Question 15

Explain how gender may increase susceptiblity to drug interactions?

Answer 15

-women are at greater risk of ADRs then men due to altered pharmacokinetics and pharmacodynamics

Question 16

Explain how concomitant disease patients more susceptible to drug interactions?

Answer 16

-multiple disease states and multiple drugs combine to cause interactions and ADRs, also altered pharmacokinetics

Question 17

Explain how ethnicity and genetics may increase susceptiblity to drug interactions?

Answer 17

-altered pharmacokinetics and pharmacodynamics
-lack of pharmaceutical company testing

Question 18

Give examples of how absorption is altered in pharmacokinetic interactions

Answer 18

-pH changes in GI tract will impact on rate and amount of drug absorption
-chemical antagonism
-gastric motility

Question 19

Give an example of how distribution is altered in pharmacokinetic interactions

Answer 19

-often occurs when two or more drugs compete for the same plasma protein, for example aspirin and warfarin

Question 20

What are the two ways in which one drug can affect the metabolism of another drug?

Answer 20

-some drugs act as inducers= speed up the activity of specific CYP450 enzymes

-some drugs act as inhibitors= slow down the activity of specific CYP450 enzymes

Question 21

What foods/ herbals are cytochrome P450 inducers?

Answer 21

-leafy green vegetables
-ethanol
-St Johns Wort
-Valerian

Question 22

What foods/ herbals are cytochrome P450 inhibitors?

Answer 22

-grapefruit juice
-cranberry juice
-watercress
-gingko biloba

Question 23

Give an example of how excretion is altered in pharmacokinetic interactions

Answer 23

-pH changes in the urine can act to speed up or slow down excretion
-competition for carriers in the renal tubule can slow excretion

Question 24

What are the 3 main pharmacodynamic interactions? and why does this happen

Answer 24

1. physiological antagonism e.g salbutamol and non-selective beta-blocker
2. synergism e.g warfarin and clopidogrel
3. interactions with food e.g MAOIs and marmite

This usually occurs when two or more drugs have the same or opposite effect