PSI Patient Counselling & Drug Interactions 3 — Questions and Answers
Question 1: A patient taking isotretinoin for severe acne must be counselled about which mandatory precaution?
- Strict contraception throughout treatment and for one month after — severe teratogen (Correct answer)
- Avoid sunlight only
- No alcohol for 2 weeks only
- Take at bedtime only
Correct answer: Strict contraception throughout treatment and for one month after — severe teratogen
Isotretinoin is teratogenic. In Ireland, the HPRA-mandated iPLEDGE-equivalent (Roaccutane/Accutane REMS) requires two forms of contraception, monthly pregnancy testing and patient agreement form.
Question 2: Which antibiotic should not be prescribed with warfarin without close INR monitoring?
- Ciprofloxacin — inhibits CYP1A2 and CYP2C9, raising warfarin levels significantly (Correct answer)
- Amoxicillin — no significant CYP interaction
- Nitrofurantoin — no CYP interaction
- Cefalexin — no CYP interaction
Correct answer: Ciprofloxacin — inhibits CYP1A2 and CYP2C9, raising warfarin levels significantly
Ciprofloxacin inhibits multiple CYP enzymes that metabolise warfarin, reducing its clearance. INR can rise substantially, increasing bleeding risk. Enhanced INR monitoring is required.
Question 3: A patient prescribed lithium is starting ibuprofen for back pain. The pharmacist should:
- Advise against ibuprofen — recommend paracetamol instead, and monitor for lithium toxicity signs (Correct answer)
- Dispense both without concern
- Halve the lithium dose automatically
- Advise stopping lithium temporarily
Correct answer: Advise against ibuprofen — recommend paracetamol instead, and monitor for lithium toxicity signs
NSAIDs reduce renal lithium clearance, raising plasma levels into the toxic range within days. Paracetamol is the safe alternative. If NSAIDs are essential, lithium levels must be monitored closely.
Question 4: Which counselling point is essential for a patient using transdermal hormone patches?
- Rotate application sites, apply to clean dry skin and press firmly for 30 seconds — avoid same site for at least one week (Correct answer)
- Apply over hairy areas for better absorption
- Remove and reapply if sweating
- Change every day regardless of the prescribed schedule
Correct answer: Rotate application sites, apply to clean dry skin and press firmly for 30 seconds — avoid same site for at least one week
Site rotation prevents skin irritation and maintains consistent drug absorption. Clean, dry, non-hairy skin (e.g., lower abdomen, upper arm) maximises adhesion. Intervals between uses of the same site allow skin recovery.
Question 5: Which combination of antibiotics produces significant risk of QT interval prolongation and ventricular arrhythmia?
- Azithromycin combined with moxifloxacin (Correct answer)
- Amoxicillin combined with metronidazole
- Doxycycline combined with nitrofurantoin
- Co-amoxiclav combined with cefalexin
Correct answer: Azithromycin combined with moxifloxacin
Both azithromycin and moxifloxacin individually prolong QT interval. Co-administration significantly increases risk of torsades de pointes — a potentially fatal ventricular arrhythmia. Avoid combining QT-prolonging agents.
Question 6: A patient requests advice on taking iron supplements. The pharmacist should advise taking iron:
- On an empty stomach with vitamin C (orange juice) to maximise absorption — if GI upset occurs, take with food (Correct answer)
- With a glass of milk
- At bedtime
- With antacids to reduce GI side effects
Correct answer: On an empty stomach with vitamin C (orange juice) to maximise absorption — if GI upset occurs, take with food
Ferrous iron absorption is maximised on an empty stomach. Vitamin C (ascorbic acid) reduces Fe3+ to Fe2+ and forms soluble chelates, enhancing absorption. Antacids, milk and tannins (tea) all reduce iron absorption.
PSI Patient Counselling & Drug Interactions 3
A patient taking isotretinoin for severe acne must be counselled about which mandatory precaution?