What is the recommended dose of Zosyn (piperacillin-tazobactam) for treating Morganella morganii infections?

Zosyn Dosing for Morganella morganii Infections

The recommended dose of Zosyn (piperacillin-tazobactam) for treating Morganella morganii infections is 4.5 g IV every 6 hours in adults with normal renal function.

Dosing Recommendations

Standard Adult Dosing:

• First-line dose: 4.5 g IV every 6 hours 1
• Administration method: Consider extended infusion (3-4 hours) instead of standard 30-minute infusions for serious infections 1

Renal Adjustment:

• CrCl 20-40 mL/min: 4.5 g IV every 8 hours 1
• CrCl <20 mL/min: 4.5 g IV every 12 hours 1
• Hemodialysis: 4.5 g IV every 12 hours, with an additional dose after each dialysis session 1

Pediatric Dosing:

• 200-300 mg/kg/day of piperacillin component divided every 6-8 hours 1
• For patients with postmenstrual age >30 weeks: 80 mg/kg/dose (of piperacillin component) IV every 6 hours, with maximum 4.5 g per dose 1

Rationale and Evidence

Morganella morganii is a gram-negative bacterium that can cause serious infections, particularly in hospitalized patients and those with compromised immune systems. M. morganii has several important resistance characteristics:

• Intrinsic resistance to first-generation cephalosporins and ampicillin-clavulanate 2
• Potential for AmpC β-lactamase production, which may affect efficacy of some antibiotics 3
• Variable resistance rates to gentamicin (30.3%), ciprofloxacin (10.1%), but low resistance to piperacillin-tazobactam (1.8%) 2

Piperacillin-tazobactam (Zosyn) is highly effective against M. morganii with very low resistance rates, making it an excellent choice for these infections 2.

Treatment Duration

• Uncomplicated infections with adequate source control: 5-7 days 1
• Complicated infections (immunocompromised patients, inadequate source control, persistent symptoms, bacteremia): 7-14 days 1

Monitoring Recommendations

• Evaluate clinical response within 48-72 hours 1
• Monitor inflammatory parameters (leukocytes, CRP, procalcitonin) 1
• Regular monitoring of renal function with dose adjustments as needed 1

Alternative Options

If M. morganii shows resistance to piperacillin-tazobactam or the patient cannot tolerate it, consider:

1. Carbapenems - most commonly used alternative treatment for M. morganii bacteremia 4

   • Meropenem: 1 g IV every 8 hours by extended infusion 5
   • Imipenem/cilastatin: 500 mg IV every 6 hours 1
   • Ertapenem: 1 g IV every 24 hours 1

2. Aminoglycosides (if susceptible) 4

   • Amikacin: 15 mg/kg/day IV once daily 5

3. Ceftazidime (if susceptible) 3

   • 2 g IV every 8 hours 5

Special Considerations

• For polymicrobial infections involving M. morganii, ensure adequate coverage for all isolated organisms 5
• In critically ill patients, consider combination therapy initially until susceptibilities are known 3
• For carbapenem-resistant strains, combination therapy may be necessary 5
• M. morganii bacteremia has a reported mortality rate of 14.7-41%, with higher risk in elderly patients and those requiring ICU admission 4, 2

Pitfalls to Avoid

• Underdosing in severe infections - use the full recommended dose
• Failure to adjust for renal function
• Inadequate source control - surgical intervention may be necessary for abscesses or other collections
• Overlooking potential drug interactions
• Insufficient treatment duration for complicated infections

Early microbiologic diagnosis and appropriate antibiotic therapy are essential for successful treatment of M. morganii infections and to prevent complications.