Does nafcillin cover Pseudomonas hauseri (P. hauseri)?

Nafcillin Does Not Cover Pseudomonas hauseri

Nafcillin does not provide coverage against Pseudomonas hauseri and should not be used for treating P. hauseri infections. 1

Understanding Nafcillin's Spectrum of Activity

Nafcillin is a penicillinase-resistant penicillin with the following characteristics:

• Primarily indicated for methicillin-susceptible Staphylococcus aureus (MSSA) infections 1
• Has no meaningful activity against gram-negative organisms, including Pseudomonas species
• Is specifically recommended for treatment of proven MSSA infections, not gram-negative infections 1

Appropriate Antibiotics for Pseudomonas Coverage

For Pseudomonas species infections, including P. hauseri, the following antibiotics should be considered:

• Antipseudomonal beta-lactams:

  • Piperacillin-tazobactam
  • Ceftazidime
  • Cefepime
  • Imipenem
  • Meropenem

• Other antipseudomonal agents:

  • Fluoroquinolones (e.g., ciprofloxacin)
  • Aminoglycosides (e.g., tobramycin, amikacin)
  • Colistin (polymyxin E)

The Infectious Diseases Society of America (IDSA) and American Thoracic Society (ATS) strongly recommend prescribing antibiotics with activity against Pseudomonas aeruginosa and other gram-negative bacilli for suspected Pseudomonas infections 1.

Clinical Implications

Using nafcillin for P. hauseri infections would result in:

• Treatment failure due to lack of antimicrobial activity
• Delayed appropriate therapy, potentially increasing morbidity and mortality
• Progression of infection

Recommended Approach for P. hauseri Infections

1. Initial empiric therapy: Start with an antipseudomonal beta-lactam (ceftazidime, cefepime, piperacillin-tazobactam, imipenem, or meropenem)

2. Consider combination therapy: For severe infections or in immunocompromised patients, consider adding a second agent from a different class (fluoroquinolone or aminoglycoside) 1

3. Adjust based on susceptibility: Modify therapy based on culture and susceptibility results

Common Pitfalls to Avoid

• Pitfall #1: Assuming all beta-lactams have similar coverage. Nafcillin is specifically designed for gram-positive coverage and lacks activity against gram-negative organisms like Pseudomonas.

• Pitfall #2: Using nafcillin for empiric therapy when gram-negative pathogens are suspected. This will result in treatment failure.

• Pitfall #3: Continuing nafcillin once P. hauseri is identified. Appropriate therapy should be promptly initiated based on susceptibility testing.

Remember that while nafcillin is an excellent choice for MSSA infections with fewer adverse effects than vancomycin 2, 3, 4, it has no role in the treatment of Pseudomonas infections of any kind.