Drug interactions Flashcards
Name THREE classes of drugs and give examples that slow down - gastric emptying (emptying of the stomach)
- Opiates - Morphine, pethidine
- Antimuscarinic drugs - Atropine, propantheline
- Tri-cyclic antidepressants - amitriptyline
Name ONE class of drugs and give examples that speed up - gastric emptying (emptying of the stomach)
Muscarinic agents - nicotine, bethanechol
How does colestyramine interact with other drugs
It binds to any acidic molecule including, thyroxine, valproate. Its purpose is just to bind to bile acid.
How does charcoal interact with other drugs?
It used to reduce absorption of digoxin, phenytoin and aspirin if taken within 1 hour can reduce up to 95% of the absorption
Some drugs cause the liver to increase in function - they cause the liver to increase to size and blood flow - this leads to increased level of P450 enzyme anction which results in increased clearance of other drugs - give examples of such drugs
Three antiepileptics - Carbamazepine, Barbituates (i.e phenobarbital) and phenytoin. Valproate doesn’t induce!! and two antimicrobials - Rifampicin and Griseofulvin
Give examples of drugs that are significantly affected by inducers
Warfarin, oral contraceptives, theophylline
What is the most serious interaction
Warfarin in not metabolised when given with phenylbutazone (patient bleeds to death). Phenylbutazone is a pain medication i.e NSAID
Give some common examples of pharmacokinetic interactions that can causing the following effects- 1. Increased hypotension, increased renal impairment
- hypotension = any two hypotensives - TCA + hypotensive (tca do interact with b-receptors). nitrate + hypotensive drug
- Renal impairment - ACEi + diuretic or NSAID
What factors affect pharmacodynamic interactions
individual differences and DNA - some people have more active enzymes than other. 2. The enzyme affects CYP2D6 or DYP3A4 or PGP. 3. The potency of the drug or induce or inhibit ( not all drugs in the same class have the same potency)
What question do you consider when doing a risk assesment and what questions do you consider when deciding on the management of interacting drugs.
- Risk assessment - how common is it? how severe are the consequences? Is it dose related?
- Management - Stop and prescribe alternative? Stop temporarily? Or monitor (i.e INR, BP, LFT or symptoms dizziness, muscle aches).
Whenever Simvastatin is prescribed what must you check for?
Itraconzole - erythromycin or clarithromycin - diltiazem or verapamil or amiodarone. tell patient to report any aches and check lipid levels.
whenever warfarin is prescribed what drugs must you check for?
Macrolides - increae INR, if it is required monitor INR in three days. 2. Tramadol - same warning as macrolides and Amiodarone - monitor INR in 4 weeks (long half life)
Whenever SSRI’s are prescribed what drugs must you check for?
TCA’s - may cause serotonin syndrome, patients needs to monitor signs of it. Tramadol - patient must be counselled on side effects of both.
What is the triple whammy and what is the management?
ACEi + diuretic + NSAID = renal failure. Avoid.
Name the EIGHT drugs to look out for when you see the following drugs prescribed tetracycline, COCs, metronidazole, lithium, sympathomimetics, adrenaline, asthmatics, MAOI’s, macrolides, SSRI’s, cardiac glycosides, nitrates.
tretracycline - antacids. COC’s - anti-epileptics. Metronidazole - alcohol. Lithium - thiazides. sympathomimemtics - beta-blockers. Adrenaline - betablockers. Asthma - beta blockers. MAOI’s tyramine (cheese, yeast, salami, chicken and beef also beer, wines and chianti. Macrolides - statins or antiepileptics (except phenytoin). SSRI’s - MAOI’s (2 weeks paroxetine and sertraline, 1 week citalopram, 5 weeks fluoxetine and 2 weeks all MAOI’s. Cardiac glycosides - diuretics or dehydration. Nitrates - sildenfil and other fils.
