What is the recommended dose of Zosyn (piperacillin/tazobactam) for a 100-pound male patient with abscess/cellulitis and normal renal function?

Zosyn Dosing for Abscess/Cellulitis in a 100 lb Male

For a 100-pound (45.4 kg) male with normal renal function and abscess/cellulitis, administer Zosyn (piperacillin-tazobactam) 3.375 grams IV every 6 hours for 5-7 days if clinical improvement occurs. 1

Standard Dosing Regimen

• The FDA-approved dose for skin and soft tissue infections including cellulitis and cutaneous abscesses is 3.375 grams (3 grams piperacillin/0.375 grams tazobactam) administered intravenously every 6 hours, totaling 13.5 grams daily 1
• Each dose should be infused over 30 minutes 1
• The usual duration of treatment is 7 to 10 days, though 5 days is sufficient if clinical improvement has occurred 1, 2

When Zosyn Is Appropriate vs. Overtreatment

Zosyn is NOT first-line therapy for typical uncomplicated cellulitis or simple abscesses. 2

• Beta-lactam monotherapy (cephalexin, dicloxacillin) succeeds in 96% of typical cellulitis cases and should be used first-line 2
• Simple abscesses require incision and drainage as primary treatment, with antibiotics playing only a subsidiary role 2

Zosyn IS appropriate for:

• Severe cellulitis with systemic toxicity (fever, hypotension, tachycardia, altered mental status) requiring broad-spectrum coverage 2
• Suspected necrotizing fasciitis or rapidly progressive infection 3, 2
• Immunocompromised or critically ill patients with inadequate source control 3
• Diabetic foot infections with moderate-to-severe severity 3

Critical Caveat: MRSA Coverage Required

Zosyn lacks activity against MRSA and must be combined with vancomycin or linezolid when used for severe infections. 2

• For severe cellulitis: Vancomycin 15-20 mg/kg IV every 8-12 hours PLUS Zosyn 3.375 grams IV every 6 hours 2
• Alternative: Linezolid 600 mg IV twice daily PLUS Zosyn 3.375 grams IV every 6 hours 2

Weight-Based Considerations

• At 100 pounds (45.4 kg), this patient falls well within normal adult dosing parameters 1
• No dose adjustment is needed based on weight alone for this patient 1
• Obesity significantly alters piperacillin pharmacokinetics (increased volume of distribution, reduced serum concentrations), but this 100 lb patient is not obese 4

Treatment Duration Algorithm

If using Zosyn for severe infection:

• Treat for 7-10 days total, reassessing at day 5 2, 1
• If clinical improvement by day 5 (reduced warmth, tenderness, erythema, afebrile), consider transitioning to oral therapy 2
• If no improvement by 48-72 hours, reassess for complications (abscess requiring drainage, necrotizing infection, resistant organisms) 2

If using Zosyn for uncomplicated infection (which is inappropriate):

• Switch to oral beta-lactam monotherapy immediately unless specific risk factors justify broad-spectrum therapy 2

Common Pitfall to Avoid

Do not use Zosyn as first-line monotherapy for typical cellulitis or simple abscess. This represents significant overtreatment, increases antibiotic resistance, and provides no benefit over standard beta-lactam therapy 2, 5, 6. Reserve Zosyn for severe infections with systemic toxicity, immunocompromise, or suspected polymicrobial/necrotizing infection where broad-spectrum coverage is genuinely indicated 3, 2.