PSI Patient Counselling & Drug Interactions 1

Question 1

Which counselling point is most important for a patient starting a new SSRI for depression?

Accepted Answer

Antidepressant effect takes 2–4 weeks — continue even if no immediate improvement

Answer

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:

Accepted Answer

Grapefruit inhibits CYP3A4 in the intestinal wall, raising simvastatin plasma levels and increasing myopathy risk

Answer

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?

Accepted Answer

Chelation — antacid cations (Al3+, Mg2+) complex with fluoroquinolones reducing oral absorption

Answer

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?

Accepted Answer

Increased phenytoin levels (risk of toxicity) — fluconazole inhibits CYP2C9

Answer

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?

Accepted Answer

Simple verbal instructions with demonstrate-and-return demonstration, written pictogram leaflets

Answer

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.

PSI Pharmacy Practice Test

PSI Pharmacy Practice Test

PSI Patient Counselling & Drug Interactions 1