Drug Interactions Flashcards
(13 cards)
What effect does sildenafil x GTN have ?[1]
What is the potential pharmacodynamic effect of aminoglycosides and loop diuretics? [1]
Both cause ototoxicity - can cause together
Rifampicin can reduce the effectiveness of which medications? [1]
Oestrogens and progesterones
Which anti-coagulant shouldn’t be paired with NSAIDs? [1]
Why? [1]
Which ONE of the following antibacterials is MOST LIKELY to reduce the effectiveness of the combined oral contraceptive when prescribed concomitantly and require women to take additional contraceptive precautions?
Amoxicillin
Cefalexin
Erythromycin
Metronidazole
Rifampicin
Differences in the body composition between males and females have the potential to make females more at risk of drug-drug interactions. Which of the following factors affecting drug pharmacokinetics is, on average higher or faster in the female sex (non-pregnant) than in the male sex?
Average organ blood flow
CYP3A4 expression
Gastro-intestinal transit
Lean muscle mass
P-glycoprotein expression
Total body water
A 44-year-old woman stabilised on the antipsychotic treatment, clozapine for the last 3 years. She has smoked 40 cigarettes a day since she was 20 years old now wants to stop. She starts nicotine replacement therapy, stops smoking cigarettes and remains on the same dose of clozapine. After few weeks she starts to experience increased sedation and therapeutic drug monitoring shows that her previously stable blood levels of clozapine have now risen into a toxic range.
Which ONE of the following interactions is most likely to be responsible for the rise in this patient’s clozapine blood levels?
Cigarette smoke induces the CYP450 enzymes which metabolise clozapine
Cigarette smoke inhibits the efflux pump which transports clozapine into the gut
Nicotine inhibits the CYP450 enzymes which metabolise clozapine
Nicotine inhibits the influx pump which transports clozapine into liver cells
Nicotine inhibits the efflux pump which transports clozapine into the gut
CYP1A2 is important for metabolism of clozapine.
The polycyclic aromatic hydrocarbons (PAHs) in cigarette smoke induce cytochrome P450 enzymes (specifically CYP1A2).
Stopping smoking reduces CYP450 enzyme activity. This can happen within days of stopping the inductive agent.
If the dose of clozapine stays the same, then the reduced CYP450 enzyme activity causes a rise in clozapine blood levels. This happens whether nicotine replacement therapy is used or not.
Smoking induces the metabolism of other CYP1A2 substrates too (e.g., olanzapine, fluvoxamine, imipramine, caffeine).
A 25-year-old woman is prescribed metronidazole 400 mg twice a day for pelvic inflammatory disease. You advise her not to drink alcohol while she is taking the metronidazole because of the potential for a disulfiram-like interaction.
What is the minimum amount of time from the last metronidazole dose that manufacturers recommend patients should abstain from alcohol after finishing a course?
24 hours
48 hours
72 hours
7 days
2 weeks
48
Which of the following food substances is most likely to reduce the effectiveness of oral ciprofloxacin and hence should not be consumed for 2 hours before or after oral ciprofloxacin administration?
Alcohol
Cranberry juice
Dairy products (e.g., milk, yoghurt)
Tyramine rich meats (e.g., salami)
Green leafy vegetables (e.g., spinach, cabbage)
Ciprofloxacin is a fluoroquinolone antimicrobial. The absorption of several oral antimicrobial agents (e.g., tetracyclines and fluoroquinolones) may be decreased by chelation with dietary cations (positively charged ions) such as calcium and magnesium in milk or other dairy products.
Chelation is also an issue when such antimicrobial agents are taken at the same time as oral iron, oral calcium, antacid, enteral feeds and oral zinc.
Other food substances listed can interact with some drugs. For example, paracetamol can increase the risk of severe liver damage when given to someone who drinks heavily; cranberry juice can increase the anticoagulant effect of warfarin; tyramine rich foods can cause potentially life-threatening hypertensive crisis in people taking monoamine oxidase inhibitors (e.g. phenelzine); the vitamin K in green leafy vegetables can reduce the anticoagulant effect of warfarin
