Zosyn (piperacillin/tazobactam) is a broad-spectrum β-lactam/β-lactamase inhibitor combination used widely in hospitals. Piperacillin covers gram-positive, gram-negative, and anaerobic bacteria, while tazobactam helps protect against β-lactamase breakdown. It is commonly used for pneumonia, intra-abdominal infections, skin and soft tissue infections, and febrile neutropenia. An important pharmacology pearl for exams is understanding that Pseudomonas, but it doesn’t cover MRSA.

The drug is renally eliminated, so dosing adjustments are needed in kidney impairment. Many institutions use extended or prolonged infusions to maximize time above the MIC, which can improve efficacy. Standard dosing is 3.375 g to 4.5 g every 6–8 hours, with modifications for dialysis patients.

Adverse effects include hypersensitivity, gastrointestinal upset, electrolyte imbalances like hypokalemia, and blood count changes with prolonged therapy. A key clinical concern is nephrotoxicity risk, especially when used with vancomycin. Monitoring renal function and electrolytes are important.

Methotrexate and probenecid are two medications that can interact with Zosyn. Concentrations of Zosyn can be increased when these medications are used in combination.

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