Pharmacology A patient develops an infection of methicillin-resistant Staphylococcus aureus. Which of the following drug cannot be used to treat the infection: A Vancomycin. B Cotrimoxazole. C Cefaclor. D Ciprofloxacin. 💡 Explanation A patient develops an infection of methicillin-resistant Staphylococcus aureus. Which of the following drug cannot be used to treat the infection: ✓ Correct Answer: C. Cefaclor.