Mupirocin and Fusidic Acid Do Not Cover Pseudomonas
Neither mupirocin nor fusidic acid (Fucidin) provide adequate coverage for Pseudomonas aeruginosa in skin infections. Both agents have narrow antimicrobial spectra targeting primarily Gram-positive organisms, particularly staphylococci and streptococci, with limited to no activity against Pseudomonas species 1, 2, 3.
Antimicrobial Spectrum of Mupirocin
- Mupirocin demonstrates excellent activity against Staphylococcus aureus (including MRSA) and most Streptococcus species 4, 1, 2
- The drug has less activity against other Gram-positive bacteria and most Gram-negative bacteria, with Pseudomonas specifically not covered 1, 5
- Mupirocin works by inhibiting bacterial isoleucyl-transfer RNA synthetase, blocking protein and RNA synthesis 5, 6
Antimicrobial Spectrum of Fusidic Acid
- Fusidic acid similarly has a narrow antibacterial spectrum focused on Gram-positive organisms, particularly staphylococci 3
- Like mupirocin, fusidic acid lacks clinically meaningful activity against Pseudomonas aeruginosa 3
When Pseudomonas Coverage Is Required
For skin infections where Pseudomonas is suspected or confirmed, you must use systemic antibiotics with antipseudomonal activity 7:
- Risk factors requiring Pseudomonas coverage include: high local prevalence of Pseudomonas infections, warm climate, frequent water exposure of the wound, or immunocompromised status 7
- Appropriate monotherapy options: carbapenems (imipenem, meropenem), antipseudomonal cephalosporins (ceftazidime, cefepime), or piperacillin-tazobactam 7
- Combination therapy alternatives: aminoglycoside plus antipseudomonal penicillin, or fluoroquinolone (ciprofloxacin) plus extended-spectrum penicillin 7
Clinical Context for Topical Agents
- Mupirocin and fusidic acid are appropriate only for superficial skin infections caused by susceptible Gram-positive organisms 4, 1, 3
- These topical agents are not appropriate for: extensive infections requiring systemic therapy, deeper soft tissue infections, or infections in immunocompromised patients 4
- For immunocompromised patients with severe skin infections, broad-spectrum coverage including antipseudomonal agents is mandatory 7
Common Pitfall to Avoid
Do not rely on topical antibiotics like mupirocin or fusidic acid for any infection where Pseudomonas is a consideration. The narrow spectrum of these agents makes them fundamentally inappropriate for Gram-negative coverage, and attempting to use them in this context will result in treatment failure 1, 2, 3.