Clindamycin is effective against many anaerobes and gram-positive cocci but does NOT reliably treat which organism?

Clindamycin lacks reliable activity against Pseudomonas aeruginosa, an aerobic gram-negative rod. Anti-pseudomonal coverage requires agents such as antipseudomonal penicillins (e.g., piperacillin), certain cephalosporins, fluoroquinolones, or aminoglycosides.Other options: Clindamycin covers anaerobes (B. fragilis, Peptostreptococcus) and many gram-positive cocci such as viridans streptococci.Key exam takeaway: Clindamycin does not cover Pseudomonas; antipseudomonal penicillins (carbenicillin/piperacillin) and select other agents do.