Pharmacology · patient case question
Clindamycin is active against each of the following EXCEPT one. Which is the EXCEPTION?
Patient case: Diarrhoea after repeated antibiotic courses
Patient: Female, 56 years old
Chief complaint: “My tooth still hurts, and now I'm having diarrhoea and stomach aches every day.”
History: Several courses of antibiotics from different physicians for tooth pain. Penicillin allergy with hives. Currently taking clindamycin.
Findings: Gross decay on tooth #30 with a chronic apical abscess. Afebrile. Reports watery diarrhoea for five days.
Show answer and explanation
Correct answer: A. Pseudomonas aeruginosa
- A. CORRECT as the exception. Clindamycin has NO activity against Pseudomonas aeruginosa, or against aerobic Gram-negative rods generally. Pseudomonas is intrinsically resistant through low outer-membrane permeability and active efflux pumps. Covering Pseudomonas requires an antipseudomonal agent — piperacillin-tazobactam, ceftazidime, cefepime, a carbapenem, or ciprofloxacin.
- B. Clindamycin covers Staphylococcus aureus well, including many community-acquired MRSA strains, which is one of its main non-dental uses.
- C. Prevotella intermedia is exactly what clindamycin is best at — Gram-negative ANAEROBES. Excellent anaerobic coverage plus good bone penetration is why it remains useful in dental infection despite its C. difficile risk.
- D. Streptococcus pneumoniae and the streptococci generally are within its spectrum, which is why it works for odontogenic infection.
Note: Clindamycin's spectrum in one line: Gram-positive cocci plus anaerobes, both Gram-positive and Gram-negative. It stops at aerobic Gram-negatives.