Metronidazole is effective against anaerobes, Helicobacter pylori, protozoa, and Trichomonas vaginalis.

• A. Clindamycin
• B. Amoxicillin
• C. Tinidazole
• D. Metronidazole

Answer: (D)

Metronidazole is the classic nitroimidazole with activity against anaerobic bacteria, Helicobacter pylori (as part of eradication regimens), and protozoa such as Trichomonas vaginalis. It works as a prodrug that, in anaerobic cells, is reduced to reactive species that damage DNA and kill the organism. This mechanism explains its selective effectiveness in anaerobes and protozoa, and why it covers the listed pathogens. Among the options, metronidazole uniquely matches this full spectrum, since the other drugs either lack activity against protozoa or do not reliably target H. pylori in practice.