Drug interactions

Question 1

What are the risk factors for drug interactions?

Answer 1

old age 
polypharmacy
lifestyle 
genetics
hepatic disease 
renal disease
narrow therapeutic index
steep dose response curve
saturable metabolism

Question 2

What factors under lifestyle are leading to increased drug interactions?

Answer 2

OTC use of drugs and supplements increasing

natural remedy use

Question 3

What are the types of drug interaction?

Answer 3

synergy
antagonism
other

Question 4

Give examples of a synergistic interaction?

Answer 4

clavulanic acid given with amoxicillin to make augmentin (a beta lactam antibiotic)
paracetamol and codeine to make co-codamol

Question 5

Give examples of drugs with a saturable metabolism

Answer 5

alcohol

paracetamol

Question 6

What are the pharmacokinetic mechanisms of drug interactions?

Answer 6

absorption
distribution
metabolism
excretion

Question 7

What are the pharmacodynamic mechanisms of drug interaction?

Answer 7

receptor based
signal transduction
physiological systems

Question 8

What are the ways in which a drug can affect absorption?

Answer 8

motility
acidity
solubility
complex formation
direct action on enterocytes

Question 9

Give an interaction that affects motility

Answer 9

antibiotics and oral contraceptive

Question 10

Give an interaction that affects acidity

Answer 10

antacids/PPIs and amprenavir (ARVT used in HIV)

Question 11

Give an interaction that affect solubility

Answer 11

avocado high fat content and anticoagulants eg avocado increases absorption of warfarin

Question 12

Give an interaction that affects complex formation

Answer 12

tetracycline binds to calcium in milk and stops tetracycline from being absorbed

Question 13

What is involved in interactions that affect distribution of drugs?

Answer 13

protein binding eg albumin

Question 14

Give two examples of interactions that affect protein binding

Answer 14

critical illness reduces albumin levels so more drug is free to bind to the receptor
sulphonamide antibiotics potentiate the effects of warfarin

Question 15

What does it mean when an drug interacts through affecting metabolism?

Answer 15

the drug induces or inhibits CYP450 enzymes

Question 16

Give an example of a drug interaction that involves inhibitions of liver enzymes

Answer 16

metronidazole inhibits alcohol dehydrogenase, so alcohol gets held up in the body as formaldehyde

Question 17

Give an example of a drug interaction that involves inhibition of liver enzymes

Answer 17

metronidazole inhibits alcohol dehydrogenase, so alcohol gets held up in the body as formaldehyde
also omeprazole inhibits the breakdown of theophylline so theophylline levels increase in the blood and this leads to cardiogenic side effects

Question 18

Give an example of an interaction that involves enzyme induction

Answer 18

clozapine is an anti-psychotic for schizophrenia and if the pt has a heart attack, the may be put on an ticlodipine which reduces platelet aggregation. Ticlodpine induces a liver enzyme so increases the breakdown on clozapine, leading to lower efficacy of the anti-psychotic

Question 19

Give examples of food that may cause interactions

Answer 19

avocado
garlic
grapefruit juice
soya
ginger

Question 20

List some drugs that grapefruit juice interacts with

Answer 20

antiarrhytmic drugs eg amiodarone
antihistamines 
Ca channel agonists 
statins eg simvastatin
immunosuppressants such as tacrolimus

Question 21

How would you treat aspirin overdose?

Answer 21

make the urine more alkaline by giving bicarbonate

Question 22

Name some drugs that are weak acids

Answer 22

aspirin, paracetamol, ibuprofen, ampicillin, warfarin, theophylline, phenytoin

Question 23

Name some drugs that are weak bases

Answer 23

atropine, amphetamine, propranolol, diazepam, salbutamol

Question 24

Give examples of receptor based pharmacodynamic interactions

Answer 24

alcohol works at the GABA A receptor as well as benzodiazepine and each have the same effect causing severe CNS depression
beta blcokers and beta agonists
buprenorphine and partial agonist given to opioid addicts

Question 25

Give examples of signal transduction interactions

Answer 25

commencing beta blockers in a diabetic, as B3 receptors sense glucose levels, so may have impaired hypoglycaemic awareness

Question 26

Give an example of an interaction that works by a physiological system

Answer 26

furosemide causes loss of K+ and digoxin’s effect is increased if there is low K+

Question 27

List ways in which interactions can be avoided

Answer 27

prescribe rationally
BNF
medicines information service
ward pharmacist
patient info leaflet 
internet