Zosyn Dosing for Acute Appendicitis
For adults with acute appendicitis, administer Zosyn (piperacillin-tazobactam) 3.375 g IV every 6 hours for uncomplicated cases requiring surgery, or 4.5 g IV every 6 hours for complicated appendicitis with adequate source control for 3-5 days maximum postoperatively. 1
Adult Dosing by Clinical Scenario
Uncomplicated Appendicitis - Surgical Management
- Single preoperative dose only: 3.375 g IV (administered 0-60 minutes before surgical incision) 2
- No postoperative antibiotics required if adequate source control achieved during appendectomy 2
- This represents the standard of care with strong evidence (Quality of Evidence: High; Strength: 1A) 2
Complicated Appendicitis - Surgical Management
- Dosing: 3.375 g IV every 6 hours 1
- Duration: Maximum 3-5 days postoperatively if adequate source control achieved 2
- Critical caveat: Prolonging antibiotics beyond 5 days offers no benefit and increases hospital stay 2
- For critically ill or immunocompromised patients, consider higher dosing: 4.5 g IV every 6 hours or 16 g/2 g continuous infusion 2
Non-Operative Management (Antibiotics-First Approach)
- Appropriate only for: CT-confirmed uncomplicated appendicitis WITHOUT appendicolith 3
- Dosing: Standard 3.375 g IV every 6 hours initially, followed by oral antibiotics for total 7-10 days 4, 5
- Success rate: Approximately 70-77% avoid surgery, but 23-39% recurrence risk over 5 years 3, 5
- High-risk features predicting failure: Appendicolith, appendiceal diameter >13 mm, mass effect (failure rates approach 40-60%) 3
Pediatric Dosing (≥2 months old)
Ages 2-9 Months
- 90 mg/kg (80 mg piperacillin/10 mg tazobactam) IV every 8 hours 1
Ages >9 Months
- 112.5 mg/kg (100 mg piperacillin/12.5 mg tazobactam) IV every 8 hours 1
- Maximum single dose should not exceed adult dosing 1
Pediatric Duration
- Uncomplicated: Single preoperative dose only 2
- Complicated: Switch to oral antibiotics after 48 hours, total duration <7 days (Quality of Evidence: Moderate; Strength: 1B) 2
Administration Details
- Infusion time: 30 minutes for all doses 1
- Renal adjustment required: If creatinine clearance ≤40 mL/min, reduce dosing frequency 1
- Do not mix with aminoglycosides: Reconstitute and administer separately; Y-site co-administration acceptable under specific conditions 1
Key Clinical Decision Points
When to avoid Zosyn entirely:
- Beta-lactam allergy (use moxifloxacin 400 mg daily or alternative regimen) 2, 4
- Recent quality improvement data shows narrow-spectrum alternatives (ceftriaxone + metronidazole) equally effective for uncomplicated cases with lower resistance pressure 6, 7
When higher dosing is justified:
- Septic shock presentation 2
- Immunocompromised or critically ill patients 2
- Inadequate or delayed source control 2
Critical pitfall to avoid: The 2020 WSES Jerusalem Guidelines explicitly recommend AGAINST routine postoperative antibiotics for uncomplicated appendicitis, yet this remains a common practice error 2. A single preoperative dose is sufficient and reduces unnecessary antibiotic exposure without increasing surgical site infections 7.
Special consideration for patients ≥40 years: If treated non-operatively, colonoscopy and interval CT scan are mandatory due to 3-17% incidence of appendiceal neoplasms 2, 4