PSI Patient Counselling & Drug Interactions 2 — Questions and Answers
Question 1: A patient is prescribed ACE inhibitor ramipril and potassium-sparing diuretic spironolactone together. The risk is:
- Hyperkalaemia — both drugs increase serum potassium (Correct answer)
- Hypokalaemia
- Hyponatraemia only
- No significant interaction
Correct answer: Hyperkalaemia — both drugs increase serum potassium
Both ACE inhibitors (reduce aldosterone-driven potassium excretion) and spironolactone (block aldosterone receptors) raise serum potassium. Combination increases hyperkalaemia risk — monitor electrolytes closely.
Question 2: When counselling a patient on oral combined contraceptive pills (COC), which advice is most important regarding missed pills?
- If 2 or more pills are missed, use additional contraception for 7 days and consider emergency contraception depending on timing (Correct answer)
- One missed pill is never a problem
- Missing pills only matters in week 3
- Missed pills have no contraceptive implications
Correct answer: If 2 or more pills are missed, use additional contraception for 7 days and consider emergency contraception depending on timing
Current FSRH guidance: if 2+ pills missed, contraceptive efficacy is reduced. Additional barrier contraception for 7 days and consideration of emergency contraception (if unprotected sex during pill-free week or start of pack) is advised.
Question 3: A patient on MAO inhibitor phenelzine is brought into the pharmacy having eaten aged cheese. They complain of severe headache. This suggests:
- Hypertensive crisis due to tyramine interaction (cheese reaction) (Correct answer)
- Migraine only
- Anaphylaxis
- Serotonin syndrome
Correct answer: Hypertensive crisis due to tyramine interaction (cheese reaction)
MAO inhibitors block breakdown of dietary tyramine (found in aged cheese, fermented foods, red wine). Tyramine accumulation causes massive noradrenaline release, causing hypertensive crisis — a potentially fatal emergency.
Question 4: Which interaction should a pharmacist counsel a patient about when dispensing sildenafil for erectile dysfunction?
- Absolute contraindication with organic nitrates (GTN, isosorbide) — risk of fatal hypotension (Correct answer)
- Avoid with statins
- Avoid with paracetamol
- Do not take with antacids
Correct answer: Absolute contraindication with organic nitrates (GTN, isosorbide) — risk of fatal hypotension
Both sildenafil (PDE-5 inhibition) and nitrates (cGMP elevation via guanylate cyclase) cause vasodilation. Combined, they produce profound, potentially fatal hypotension. Nitrates are an absolute contraindication.
Question 5: A patient on warfarin asks about taking cranberry juice. The pharmacist should advise:
- Avoid large amounts — cranberry juice may inhibit CYP2C9, raising warfarin levels and INR (Correct answer)
- Cranberry is completely safe in any amount with warfarin
- A small glass is a safe daily limit
- Cranberry reduces warfarin efficacy
Correct answer: Avoid large amounts — cranberry juice may inhibit CYP2C9, raising warfarin levels and INR
Cranberry juice, especially in large quantities, may inhibit CYP2C9 (warfarin's main metabolic pathway), increasing INR and bleeding risk. Case reports and pharmacovigilance data support caution with regular large intakes.
Question 6: Which counselling point must be given to a patient starting metronidazole?
- Avoid alcohol completely during treatment and for 48 hours after — causes disulfiram-like reaction (Correct answer)
- Take with alcohol to improve taste
- Safe to drink beer in moderation
- Alcohol has no interaction with metronidazole
Correct answer: Avoid alcohol completely during treatment and for 48 hours after — causes disulfiram-like reaction
Metronidazole inhibits acetaldehyde dehydrogenase. Alcohol consumption causes acetaldehyde accumulation producing flushing, nausea, vomiting, palpitations and hypotension — the disulfiram-like reaction.
PSI Patient Counselling & Drug Interactions 2
A patient is prescribed ACE inhibitor ramipril and potassium-sparing diuretic spironolactone together.
The risk is: