What is the recommended treatment for Morganella morganii infection in a patient allergic to penicillin (pcn)?

Treatment of Morganella morganii Infection in Penicillin-Allergic Patients

For patients allergic to penicillin, carbapenems (imipenem-cilastatin or meropenem) are the first-line treatment for Morganella morganii infections due to their excellent efficacy and low cross-reactivity with penicillin allergy. 1, 2

First-Line Treatment Options

Carbapenems

• Imipenem-cilastatin: FDA-approved for treating infections caused by Morganella morganii, including urinary tract, intra-abdominal, skin/skin structure infections, and bacteremia 1, 2
• Meropenem: Effective alternative with similar spectrum of activity 3

For Patients with Severe (Type I) Penicillin Allergy

If true anaphylactic reaction to penicillin is documented and carbapenems cannot be used:

1. Fluoroquinolones + Aminoglycosides combination:

   • Ciprofloxacin plus gentamicin or amikacin 3, 4

2. Ceftazidime (if no immediate hypersensitivity reaction to penicillin):

   • Most M. morganii isolates (95.8%) are susceptible to ceftazidime 5
   • True cross-reactivity between penicillins and cephalosporins is only approximately 2% 6

Treatment Algorithm

1. Assess penicillin allergy severity:

   • Non-severe allergy (delayed rash): Consider carbapenem (imipenem-cilastatin)
   • Severe allergy (anaphylaxis, angioedema): Use non-β-lactam alternatives

2. First-line treatment:

   • Imipenem-cilastatin: FDA-approved for M. morganii infections 1, 2

3. Alternative regimens (if carbapenems contraindicated):

   • Fluoroquinolone + Aminoglycoside: Ciprofloxacin plus gentamicin or amikacin 4
   • Ceftazidime (if no immediate hypersensitivity to penicillin) 5
   • Tigecycline (for polymicrobial infections, though limited activity against M. morganii) 3

Important Considerations

Antibiotic Resistance Patterns

• M. morganii shows universal resistance to cephalothin and high resistance to cefuroxime (90.5%) and amoxicillin-clavulanate (95.9%) 5
• Increasing reports of carbapenem-resistant strains (19.4% imipenem-resistant in one study) 5
• Recent studies show emergence of highly multidrug-resistant M. morganii producing NDM-type metallo-β-lactamases 7

Risk Factors for Mortality

• Inappropriate antibiotic therapy is the most significant independent risk factor for mortality (OR 4.8) 5
• Other risk factors include diabetes mellitus and polymicrobial bacteremia 5
• Overall mortality rate from M. morganii bacteremia can be as high as 38.3% 5

Infection Control

• M. morganii infections are often nosocomial or postoperative 4
• More common in immunocompromised patients and those with underlying conditions 8

Clinical Pearls

• Always obtain cultures and susceptibility testing to guide definitive therapy
• Consider formal penicillin allergy testing for patients with vague allergy history, as approximately 90% of patients with reported penicillin allergy are not truly allergic 6
• For severe infections, combination therapy may be necessary until susceptibility results are available
• Carbapenem-sparing regimens should be considered when appropriate to reduce selective pressure for carbapenem-resistant organisms 3