What is the recommended treatment for a male patient with a Morganella morganii urinary tract infection (UTI)?

Treatment of Morganella morganii Urinary Tract Infection in Males

For male patients with Morganella morganii urinary tract infection, a carbapenem (such as imipenem, meropenem, or ertapenem) is the recommended first-line treatment due to high rates of resistance to other antibiotics.

Antimicrobial Selection

First-line Options:

• Carbapenems:
  • Imipenem-cilastatin: 1g IV every 6-8 hours
  • Meropenem: 1g IV every 8 hours
  • Ertapenem: 1g IV once daily

Alternative Options (based on susceptibility testing):

• Aminoglycosides:

  • Amikacin: 15 mg/kg/day IV
  • Gentamicin: 5 mg/kg/day IV

• Third-generation cephalosporins:

  • Ceftazidime: 2g IV every 8 hours (if susceptible)

• Fluoroquinolones (if susceptible):

  • Ciprofloxacin: 500-750mg PO twice daily or 400mg IV every 12 hours

Treatment Algorithm

1. Initial Assessment:

   • Obtain urine culture with antimicrobial susceptibility testing before starting antibiotics
   • Assess for signs of systemic infection or sepsis
   • Evaluate for urinary tract obstruction with imaging (ultrasound or CT)

2. Initial Empiric Therapy:

   • Start with a carbapenem while awaiting culture results
   • Consider IV therapy initially, especially if signs of systemic infection

3. Directed Therapy (after susceptibility results):

   • Adjust antibiotics based on susceptibility testing
   • Consider oral step-down therapy if patient is improving and organism is susceptible

4. Duration of Treatment:

   • 7-14 days for uncomplicated UTI
   • 14-21 days for complicated UTI or pyelonephritis

Rationale and Evidence

M. morganii is known for its high resistance rates to multiple antibiotics. Recent studies show significant resistance to:

• Ciprofloxacin
• Trimethoprim-sulfamethoxazole
• Nitrofurantoin
• Amoxicillin/clavulanate
• First and second-generation cephalosporins 1

A systematic review of M. morganii infections found that most isolates were susceptible to ceftazidime, imipenem, and amikacin 2. The mortality rate for M. morganii bacteremia can be as high as 38.3%, with inappropriate antibiotic treatment being the most significant risk factor for mortality 3.

Male UTIs are classified as complicated infections due to anatomical differences and higher likelihood of underlying structural abnormalities 4. This classification necessitates more aggressive treatment approaches.

Special Considerations

Resistance Patterns

M. morganii naturally produces AmpC β-lactamases, conferring resistance to:

• Ampicillin
• First-generation cephalosporins (100% resistance to cephalothin)
• Second-generation cephalosporins (90.5% resistance to cefuroxime)
• Amoxicillin-clavulanate (95.9% resistance) 3

Evaluation for Underlying Conditions

• Consider urological evaluation for structural abnormalities
• Assess for potential sources of infection (prostatic involvement, stones)
• Evaluate for immunocompromising conditions that may predispose to M. morganii infection

Follow-up

• Repeat urine culture after completion of therapy to ensure eradication
• Consider imaging to rule out structural abnormalities if this is the first episode of UTI in a male patient
• Bacterial persistence in males often indicates underlying structural or functional abnormalities that require evaluation 4

Pitfalls to Avoid

1. Do not use empiric treatment with fluoroquinolones without susceptibility testing due to increasing resistance rates
2. Do not use nitrofurantoin for M. morganii UTIs as it has poor activity against this organism
3. Do not delay treatment in patients with signs of systemic infection or sepsis
4. Do not forget to evaluate for urinary obstruction which can complicate treatment and lead to treatment failure
5. Do not use trimethoprim-sulfamethoxazole empirically due to high resistance rates

By following this treatment algorithm and considering the special characteristics of M. morganii infections in male patients, clinicians can optimize outcomes and reduce the risk of treatment failure and complications.