A 55-year-old man with chronic sinusitis presents with fever, headache, focal neurological deficit and progressive drowsiness. Contrast MRI shows a frontal lobe ring-enhancing lesion, and needle aspiration reveals mixed infection with obligate anaerobes including Peptostreptococcus. Metronidazole is chosen partly because of which distinctive distribution property?

• A Exclusive confinement to the extracellular fluid compartment
• B Binding to bone hydroxyapatite achieving osteomyelitis-level concentrations
• C Selective concentration only within phagocytes at inflamed sites
• D Excellent penetration into brain tissue, CSF and abscess cavities irrespective of meningeal inflammation ✓

Explanation

Metronidazole is small, lipophilic and minimally protein bound, giving it near-complete bioavailability and excellent diffusion into CSF, brain parenchyma and abscess pus even without inflamed meninges, which makes it a mainstay alongside a third-generation cephalosporin in anaerobic brain abscess. Intracellular concentration is a macrolide trait, and bone binding describes clindamycin and fluoroquinolones rather than metronidazole.

Reference: Katzung Basic and Clinical Pharmacology, 15th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.