PSI Patient Counselling & Drug Interactions 1 — Questions and Answers
Question 1: Which counselling point is most important for a patient starting a new SSRI for depression?
- Antidepressant effect takes 2–4 weeks — continue even if no immediate improvement (Correct answer)
- Stop the medication if side effects occur in week 1
- SSRIs work immediately
- Take double dose if you miss a day
Correct answer: Antidepressant effect takes 2–4 weeks — continue even if no immediate improvement
SSRIs take 2–4 weeks for full antidepressant effect. Early discontinuation is a major cause of treatment failure. Patients must be counselled to persist through initial side effects and not expect immediate results.
Question 2: A patient asks why they must avoid grapefruit juice with their simvastatin. The pharmacist explains:
- Grapefruit inhibits CYP3A4 in the intestinal wall, raising simvastatin plasma levels and increasing myopathy risk (Correct answer)
- Grapefruit reduces simvastatin absorption
- Grapefruit increases renal excretion of simvastatin
- Grapefruit causes a taste interaction only
Correct answer: Grapefruit inhibits CYP3A4 in the intestinal wall, raising simvastatin plasma levels and increasing myopathy risk
Grapefruit contains furanocoumarins that irreversibly inhibit intestinal CYP3A4, increasing oral bioavailability of simvastatin. This raises plasma levels, increasing the risk of myopathy and rhabdomyolysis.
Question 3: Which drug interaction mechanism underlies the interaction between antacids and fluoroquinolone antibiotics?
- Chelation — antacid cations (Al3+, Mg2+) complex with fluoroquinolones reducing oral absorption (Correct answer)
- Antacids induce CYP enzymes
- Competition for protein binding
- Fluoroquinolones inhibit antacid neutralisation
Correct answer: Chelation — antacid cations (Al3+, Mg2+) complex with fluoroquinolones reducing oral absorption
Divalent and trivalent metal cations form insoluble chelates with fluoroquinolones (and tetracyclines), preventing absorption. Fluoroquinolones should be taken 2 hours before or 6 hours after antacids.
Question 4: A patient on phenytoin is started on fluconazole. Which outcome should the pharmacist anticipate?
- Increased phenytoin levels (risk of toxicity) — fluconazole inhibits CYP2C9 (Correct answer)
- Decreased phenytoin levels
- No interaction — phenytoin levels unchanged
- Fluconazole levels increase only
Correct answer: Increased phenytoin levels (risk of toxicity) — fluconazole inhibits CYP2C9
Fluconazole is a potent CYP2C9 inhibitor. Phenytoin is primarily metabolised by CYP2C9. Combination leads to significantly elevated phenytoin levels, risking ataxia, nystagmus and diplopia.
Question 5: Which patient counselling approach best ensures medication adherence in a patient with low health literacy?
- Simple verbal instructions with demonstrate-and-return demonstration, written pictogram leaflets (Correct answer)
- Providing a detailed written clinical summary
- Referring all low-literacy patients to a specialist
- Only verbal instructions in a loud, clear voice
Correct answer: Simple verbal instructions with demonstrate-and-return demonstration, written pictogram leaflets
Low health literacy requires plain language, demonstration, teach-back and visual aids. Complex written materials are ineffective. Combination verbal and pictogram approaches significantly improve comprehension.
Question 6: Which drug interaction between methotrexate and NSAIDs is clinically significant?
- NSAIDs reduce renal methotrexate clearance, causing toxicity (mucositis, myelosuppression) (Correct answer)
- NSAIDs reduce methotrexate absorption
- NSAIDs enhance methotrexate efficacy safely
- No clinically relevant interaction
Correct answer: NSAIDs reduce renal methotrexate clearance, causing toxicity (mucositis, myelosuppression)
NSAIDs inhibit prostaglandin-mediated renal blood flow, reducing GFR and methotrexate excretion. This can cause severe, life-threatening methotrexate toxicity even at low weekly rheumatological doses.
PSI Patient Counselling & Drug Interactions 1
Which counselling point is most important for a patient starting a new SSRI for depression?