Pharmacist Flashcards

A patient on warfarin is started on fluconazole for a fungal infection. Which mechanism best explains the resulting increase in warfarin's anticoagulant effect?

Answer: Fluconazole inhibits CYP2C9, reducing warfarin metabolism and elevating plasma concentrations

Warfarin (particularly the S-enantiomer) is primarily metabolized by CYP2C9. Fluconazole is a potent CYP2C9 inhibitor, which significantly reduces warfarin clearance, leading to elevated plasma levels and an increased anticoagulant effect. This interaction necessitates close INR monitoring and often a warfarin dose reduction.

A pharmacist receives a prescription for methotrexate 25 mg orally once weekly for rheumatoid arthritis. The patient is also prescribed trimethoprim-sulfamethoxazole (TMP-SMX). What is the PRIMARY pharmacodynamic concern with this combination?

Answer: Both drugs inhibit dihydrofolate reductase, leading to additive folate depletion and severe toxicity

Both methotrexate and trimethoprim inhibit dihydrofolate reductase (DHFR). When used concurrently, this produces additive antifolate effects, dramatically increasing the risk of bone marrow suppression, mucositis, and pancytopenia. This combination should generally be avoided; if unavoidable, intensive monitoring and leucovorin supplementation are required.

Under DHA regulations, a pharmacist is counseling a patient on semaglutide (Ozempic) 0.5 mg subcutaneous weekly for type 2 diabetes. The patient asks if the pen can be stored in the car in Dubai's summer heat. What is the correct storage guidance for an in-use pen?

Answer: An in-use pen can be kept at room temperature up to 30°C for up to 56 days, away from direct sunlight

Once in use, semaglutide injection pens (Ozempic) can be stored at room temperature not exceeding 30°C for up to 56 days. A car in Dubai's summer heat can easily exceed 50°C, rendering this storage inappropriate. The pharmacist must advise against in-car storage and explain the 30°C ceiling and 56-day limit for opened pens.

A 68-year-old male with CKD stage 4 (eGFR 22 mL/min/1.73m²) is prescribed gabapentin 300 mg three times daily for diabetic neuropathy. What is the most appropriate pharmacist intervention?

Answer: Flag the prescription for dose reduction, as gabapentin is renally eliminated and accumulates in CKD

Gabapentin is almost entirely renally eliminated without hepatic metabolism. In CKD stage 4 (eGFR 15–29), significant dose reduction is mandatory. A typical recommendation is gabapentin 100–300 mg once or twice daily rather than three times daily, to prevent accumulation causing CNS toxicity (sedation, confusion, respiratory depression). Pregabalin also requires renal dose adjustment, making option B incorrect.

A pharmacist is verifying a pediatric prescription for amoxicillin-clavulanate (Augmentin) for a 4-year-old child weighing 16 kg diagnosed with acute otitis media unresponsive to standard amoxicillin. The prescription reads: amoxicillin component 90 mg/kg/day divided every 12 hours. Which formulation is most appropriate to minimize clavulanate-associated GI adverse effects?

Answer: Augmentin ES-600 suspension (600 mg/5 mL amoxicillin with fixed 42.9 mg clavulanate per 5 mL) to deliver high-dose amoxicillin while limiting excess clavulanate

For high-dose amoxicillin therapy (80–90 mg/kg/day) in resistant otitis media, Augmentin ES-600 is specifically formulated to deliver a high amoxicillin concentration (600 mg/5 mL) with a proportionally lower clavulanate amount per dose. This limits the clavulanate-related GI adverse effects (diarrhea, nausea) that would occur if the standard 250:62.5 or 400:57 formulations were used to reach the same amoxicillin target — which would require larger volumes and deliver excessive clavulanate.

A pharmacist notices a prescription for lithium carbonate 900 mg twice daily in a patient who was recently started on hydrochlorothiazide 25 mg daily for hypertension. Which of the following best explains the mechanism of the clinically significant interaction requiring lithium level monitoring?

Answer: Thiazides cause natriuresis; compensatory proximal tubular reabsorption of sodium also reabsorbs lithium, raising serum levels

Lithium is not protein-bound or hepatically metabolized; it is handled by the kidney similarly to sodium. Thiazide diuretics promote sodium excretion, triggering compensatory reabsorption of both sodium and lithium in the proximal tubule. This reduces lithium clearance and can raise serum lithium levels into the toxic range (>1.5 mEq/L). The pharmacist should alert the prescriber and recommend lithium level monitoring within 5–7 days of starting the thiazide.