Treatment of Mycobacterium abscessus Skin and Soft Tissue Infections
For serious M. abscessus skin and soft tissue infections, treat with combination therapy using clarithromycin (1,000 mg/day) or azithromycin (250 mg/day) plus parenteral amikacin (10-15 mg/kg IV daily), with or without cefoxitin (up to 12 g/day IV) or imipenem (500 mg 2-4 times daily IV), for a minimum of 4 months. 1
Initial Treatment Approach
Combination therapy is mandatory to prevent macrolide resistance development, which can occur rapidly with monotherapy due to M. abscessus having only a single copy of the 23S rRNA gene 1
Macrolides are the cornerstone oral agents as they are the only oral drugs reliably active against M. abscessus in vitro, with clarithromycin showing 100% susceptibility 1
Amikacin is the most active parenteral agent and should be dosed at 10-15 mg/kg IV daily in adults with normal renal function to achieve peak serum levels around 20 mg/mL 1
Add high-dose cefoxitin (up to 12 g/day IV in divided doses) or imipenem (500 mg 2-4 times daily IV) as the second parenteral agent for initial therapy (minimum 2 weeks) until clinical improvement is evident 1
Treatment Duration and Surgery
Minimum 4 months of therapy is necessary to provide a high likelihood of cure for serious skin and soft tissue disease 1
For bone infections, extend therapy to 6 months 1
Surgery is generally indicated with extensive disease, abscess formation, or where drug therapy is difficult 1
Removal of foreign bodies is essential to recovery, including breast implants, percutaneous catheters, or any other prosthetic material 1
Critical Susceptibility Patterns
M. abscessus isolates demonstrate the following susceptibility patterns that guide therapy selection:
- Clarithromycin: 100% susceptible (but inducible resistance via erm(41) gene is common) 1, 2
- Amikacin: 90% susceptible 1, 2
- Cefoxitin: 70% susceptible 1
- Imipenem: 50% susceptible (though testing reliability is limited) 1
- Linezolid: 50% susceptible or intermediate 1
Important Caveats and Pitfalls
Avoid these common mistakes:
Never use macrolide monotherapy for serious infections, as this rapidly selects for resistance through mutations in the 23S rRNA gene 1
M. abscessus is uniformly resistant to standard antituberculous agents (isoniazid, rifampin, ethambutol, pyrazinamide), so do not use typical TB regimens 1
Distinguish M. abscessus from M. chelonae, as M. chelonae is potentially easier to treat and has different susceptibility patterns (M. chelonae is uniformly resistant to cefoxitin but susceptible to tobramycin) 1
Antibiotic susceptibility testing of all clinically significant isolates is mandatory due to variable drug susceptibilities 1
Inducible macrolide resistance is a major concern: approximately 46% of isolates carry the full-length erm(41) gene conferring inducible clarithromycin resistance 2, 3
Alternative and Adjunctive Agents
For patients who cannot tolerate standard therapy or have resistant isolates:
Linezolid (600 mg daily) shows activity in approximately 50% of isolates and may be used as an alternative, though long-term use at 600 mg twice daily causes severe side effects (anemia, peripheral neuropathy) 1
Tigecycline has in vitro activity and most strains are susceptible, but must be given intravenously and causes nausea and anorexia with long-term use 1, 2
Clofazimine shows low MICs but methodology and breakpoints are not yet standardized 1
Monitoring and Follow-up
Monitor amikacin levels to ensure therapeutic peaks and avoid toxicity, especially with prolonged therapy 1
Watch for macrolide resistance emergence during therapy, particularly in isolates with the erm(41) gene 2, 3
Clinical improvement should be evident within 2 weeks of initiating parenteral therapy; if not, reassess surgical options 1