piperacillin/tazobactam
Summary
Piperacillin-tazobactam is an extended-spectrum beta-lactam/beta-lactamase inhibitor combination antibiotic with broad coverage including Pseudomonas aeruginosa, gram-positive, gram-negative, and anaerobic organisms. It is commonly used empirically for severe hospital-acquired infections, intra-abdominal infections, and febrile neutropenia.
Detail
Piperacillin is an extended-spectrum ureidopenicillin that inhibits bacterial cell wall synthesis by binding penicillin-binding proteins (PBPs), disrupting peptidoglycan cross-linking. Tazobactam is a beta-lactamase inhibitor that irreversibly inhibits many bacterial beta-lactamase enzymes, protecting piperacillin from degradation and extending its spectrum to beta-lactamase-producing organisms. The combination provides broad-spectrum coverage against gram-positive organisms (including Streptococcus and some Enterococcus species, but not MRSA), gram-negative organisms (including Pseudomonas aeruginosa, Enterobacteriaceae), and anaerobes (including Bacteroides fragilis). It does not reliably cover ESBL- or carbapenemase-producing organisms, atypicals, or MRSA.
Clinical uses include empiric treatment of nosocomial pneumonia, intra-abdominal infections, complicated skin/soft tissue infections, febrile neutropenia, and sepsis of unknown source, especially when Pseudomonas coverage is needed. It is often combined with vancomycin for empiric MRSA coverage in severe infections.
Key adverse effects include hypersensitivity reactions (cross-reactivity with other penicillins), interstitial nephritis, cytopenias (especially neutropenia with prolonged use), electrolyte disturbances (sodium overload, hypokalemia from non-reabsorbable anion effect), and potential interference with platelet function causing bleeding risk. There has been clinical controversy regarding increased acute kidney injury when combined with vancomycin (piperacillin-tazobactam + vancomycin nephrotoxicity), which is tested on exams as a classic 'pseudo-AKI' phenomenon affecting creatinine clearance measurement via tubular secretion inhibition, though true nephrotoxicity mechanisms are still debated.
Mechanistically, it's important for boards to know: beta-lactams are bactericidal, time-dependent killers requiring frequent dosing or prolonged infusions to maximize time above MIC. Resistance arises via altered PBPs, efflux pumps, or production of beta-lactamases not inhibited by tazobactam (e.g., ESBLs, AmpC, carbapenemases).
Sources
- First Aid for the USMLE Step 1
- Katzung's Basic and Clinical Pharmacology
- Sanford Guide to Antimicrobial Therapy
- UpToDate: Piperacillin-tazobactam
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