ADRs and drug interactions Flashcards
What are the types of drug-disease interactions?
1) drug-herbal medicine interactions
2) drug-disease interactions
3) drug-food/drink interactions
What herbal medicine used for the treatment of depression interacts with a lot of medicines?
St John’s Wort
cautions
when a drug can be used in a patient with another specific medical condition but with caution
contraindications
when a drug must not be used in patients with another specific medical condition
What resources can you use to check whether a drug interacts with food or drink?
1) Stockley’s Drug Interactions
2) Cautionary and Advisory labels that appear on dispensing labels
3) summary of product characteristics (SPC) on medicines.org.uk/emc#gref
monoamine oxidase inhibitors (MAOIs)
a type of specialist use only antidepressant
Give some examples of MAOIs.
1) phenelzine
2) moclobemide
3) tranylcypromine
4) isocarboxazid
5) linezoid (antibiotic)
What do MAOIs interact with?
tyramine-containing foods
sympathomimetic
producing physiological effects characteristic of the sympathetic nervous system by promoting the stimulation of sympathetic nerves
How does tyramine act in the body?
liberates stored catecholamines
What are the effects of tyramine?
1) potentially fatal hypertensive crisis
2) arrhythmias
3) hyperthermia
4) cerebral haemorrhage
5) severe headache
What foods should patients on MAOIs avoid as they contain a high tyramine content?
1) aged meat/fish
2) stale
3) fermented
4) overly ripe
5) pickled
6) mature cheeses
7) yeast extracts
8) fermented soya bean products
9) offal
10) game
11) yoghurt
12) sour cream
13) cured meats
14) sauerkraut
15) miso soup
16) OXO
17) bovril
18) marmite
19) broad beans
20) excessive amounts of chocolate
What drinks should patients on MAOIs avoid?
1) undistilled alcoholic beverages
2) wine
3) beer
4) lager
5) excessive amounts of tea and coffee
How long does the interaction between food/drink + MAOIs persist after treatment is stopped?
2 weeks
Why does grapefruit/grapefruit juice interact with lots of different drugs?
grapefruit juice can block the action of CYP3A4 (by which many drugs are metabolised) leading to higher levels of the drug in the bloodstream
How does Natto, a japanese food made from fermented soya bean, reduce the effects of warfarin?
high levels of vitamin K2 are produced in the fermentation process
How does cranberry juice affect the anticoagulant effect of warfarin?
cranberry juice increases the INR of patients taking warfarin
How does alcohol affect warfarin?
heavy drinkers of alcohol may have a reduced response to coumarins + binge drinking may increase the risk of bleeding. this is because continuous heavy drinking stimulates the hepatic enzymes concerned with the metabolism of warfarin, leading to more rapid elimination
bisphosphonates
drugs that help to strengthen bones + reduce the risk of a bone breaking
What can impair absorption of bisphosphonates?
bisphosphonates can form complexes with a number of polyvalent metallic ions in food
How should bisphosphonates be taken?
1) after an overnight fast
2) patients should wait at least 30 minutes to take any other drug/food
3) with plain water only while sitting/standing
4) tablets swallowed whole
5) oral solution swallowed as a single dose
Why do bisphosphonates need to be taken with plenty of water whilst the patient is upright?
to reduce the risk of ulcers + bleeding
How does dairy affect tetracyclines?
it binds calcium and iron, forming insoluble chelates, reducing its bioavailability
How does dairy affect quinolones?
milk + yoghurt reduce the concentrations of ciprofloxacin by up to about 50%
