Canadian Pharmacist Qualifying Exam Practice · Question
A patient taking warfarin is prescribed a new antibiotic. Which antibiotic class is known to significantly increase INR by inhibiting CYP2C9?
Sulfonamides like cotrimoxazole (trimethoprim/sulfamethoxazole) are potent inhibitors of CYP2C9, which metabolizes warfarin, leading to increased INR and bleedi
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Question: A patient taking warfarin is prescribed a new antibiotic. Which antibiotic class is known to significantly increase INR by inhibiting CYP2C9?
Answer options:
- Cephalosporins
- Fluoroquinolones
- Macrolides ✅ Sulfonamides (e.g., cotrimoxazole)
Correct answer: Sulfonamides (e.g., cotrimoxazole)
Explanation: Sulfonamides like cotrimoxazole (trimethoprim/sulfamethoxazole) are potent inhibitors of CYP2C9, which metabolizes warfarin, leading to increased INR and bleeding risk.
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