Drug interactions Flashcards
What are the risk factors for drug interactions?
old age polypharmacy lifestyle genetics hepatic disease renal disease narrow therapeutic index steep dose response curve saturable metabolism
What factors under lifestyle are leading to increased drug interactions?
OTC use of drugs and supplements increasing
natural remedy use
What are the types of drug interaction?
synergy
antagonism
other
Give examples of a synergistic interaction?
clavulanic acid given with amoxicillin to make augmentin (a beta lactam antibiotic)
paracetamol and codeine to make co-codamol
Give examples of drugs with a saturable metabolism
alcohol
paracetamol
What are the pharmacokinetic mechanisms of drug interactions?
absorption
distribution
metabolism
excretion
What are the pharmacodynamic mechanisms of drug interaction?
receptor based
signal transduction
physiological systems
What are the ways in which a drug can affect absorption?
motility acidity solubility complex formation direct action on enterocytes
Give an interaction that affects motility
antibiotics and oral contraceptive
Give an interaction that affects acidity
antacids/PPIs and amprenavir (ARVT used in HIV)
Give an interaction that affect solubility
avocado high fat content and anticoagulants eg avocado increases absorption of warfarin
Give an interaction that affects complex formation
tetracycline binds to calcium in milk and stops tetracycline from being absorbed
What is involved in interactions that affect distribution of drugs?
protein binding eg albumin
Give two examples of interactions that affect protein binding
critical illness reduces albumin levels so more drug is free to bind to the receptor
sulphonamide antibiotics potentiate the effects of warfarin
What does it mean when an drug interacts through affecting metabolism?
the drug induces or inhibits CYP450 enzymes
Give an example of a drug interaction that involves inhibitions of liver enzymes
metronidazole inhibits alcohol dehydrogenase, so alcohol gets held up in the body as formaldehyde
Give an example of a drug interaction that involves inhibition of liver enzymes
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
Give an example of an interaction that involves enzyme induction
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
Give examples of food that may cause interactions
avocado garlic grapefruit juice soya ginger
List some drugs that grapefruit juice interacts with
antiarrhytmic drugs eg amiodarone antihistamines Ca channel agonists statins eg simvastatin immunosuppressants such as tacrolimus
How would you treat aspirin overdose?
make the urine more alkaline by giving bicarbonate
Name some drugs that are weak acids
aspirin, paracetamol, ibuprofen, ampicillin, warfarin, theophylline, phenytoin
Name some drugs that are weak bases
atropine, amphetamine, propranolol, diazepam, salbutamol
Give examples of receptor based pharmacodynamic interactions
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
Give examples of signal transduction interactions
commencing beta blockers in a diabetic, as B3 receptors sense glucose levels, so may have impaired hypoglycaemic awareness
Give an example of an interaction that works by a physiological system
furosemide causes loss of K+ and digoxin’s effect is increased if there is low K+
List ways in which interactions can be avoided
prescribe rationally BNF medicines information service ward pharmacist patient info leaflet internet
