A patient needing treatment for Helicobacter pylori to be taken alongside amoxicillin and omeprazole at a dose of 400 mg twice daily. Which antibiotic is most appropriate for the presenting condition?

• A. Metronidazole
• B. Amoxicillin
• C. Clarithromycin
• D. Moxifloxacin

Answer: (A)

When treating Helicobacter pylori, the regimen combines a proton pump inhibitor with antibiotics, chosen partly by how each drug is dosed in standard regimens. The option given to pair with amoxicillin and omeprazole at 400 mg twice daily is metronidazole, because metronidazole is commonly prescribed for H. pylori at a dose of 400 mg taken twice daily in many regimens. Other antibiotics shown—clarithromycin is typically given at around 500 mg twice daily, moxifloxacin is usually given as 400 mg once daily, and amoxicillin is generally given in higher doses as part of the combination—so the 400 mg twice-daily dose fits metronidazole, making it the best choice. Remember that regimens with metronidazole are used in various combinations (such as quadruple therapy with other agents) to overcome resistance and improve eradication.