Which antibiotic is NOT effective against Pseudomonas aeruginosa?

Correct answer: B. Clindamycin

• A. Ceftazidime is the anti-pseudomonal third-generation cephalosporin — distinguishing it from ceftriaxone, which is not.
• B. CORRECT. CLINDAMYCIN has NO activity against Pseudomonas aeruginosa. Its spectrum covers gram-positive cocci and ANAEROBES — which is exactly why it is useful in odontogenic infection and in penicillin-allergic patients, and equally why it fails against this gram-negative aerobe. Pseudomonas is intrinsically resistant through porin restriction and efflux pumps.
• C. Ciprofloxacin is one of the classic anti-pseudomonal agents and the main oral option available for it.
• D. Piperacillin-tazobactam is a first-line anti-pseudomonal beta-lactam combination.

Note: Anti-pseudomonal agents worth knowing: ciprofloxacin and levofloxacin, piperacillin-tazobactam, ceftazidime and cefepime, the carbapenems (except ertapenem), and the aminoglycosides.