Treatment for Mycobacterium abscessus Infections
The treatment of Mycobacterium abscessus infections requires a two-phase approach with an initial intensive phase of intravenous antibiotics (amikacin, imipenem or cefoxitin, and possibly tigecycline) combined with an oral macrolide (preferably azithromycin), followed by a continuation phase with oral and inhaled antibiotics for extended periods. 1
Initial Intensive Phase Treatment
The initial intensive phase aims to rapidly decrease bacterial load using:
Intravenous antibiotics (for 3-12 weeks):
- Amikacin IV (10-15 mg/kg/day for patients <50 years; 10 mg/kg/day for patients >50 years) 1
- Plus one or more of the following:
- Imipenem IV (500 mg 2-4 times daily) - preferred over cefoxitin due to better side effect profile 1
- Cefoxitin IV (up to 12 g/day divided doses) - note that 60% of patients may require discontinuation due to toxicity 1
- Tigecycline IV - has low MIC against M. abscessus but often causes significant nausea and vomiting 1, 2
Combined with oral therapy:
- Azithromycin (preferred over clarithromycin as it's a weaker inducer of erm gene) 1
The duration of the intensive phase depends on disease severity, treatment response, and regimen tolerability, typically ranging from 3-12 weeks 1.
Continuation Phase Treatment
After the intensive phase, transition to:
- Oral macrolide (preferably azithromycin) 1
- Inhaled amikacin 1, 3
- 2-3 additional oral antibiotics from:
- Minocycline
- Clofazimine
- Moxifloxacin
- Linezolid 1
Important Considerations
Subspecies Identification
Identifying the M. abscessus subspecies is critical as treatment outcomes differ significantly:
- M. abscessus subspecies massiliense (lacking functional erm41 gene) has better treatment outcomes with cure rates of 91% 3, 4
- M. abscessus subspecies abscessus (with functional erm41 gene) has lower cure rates of only 31% 3, 4
Macrolide Resistance
- Strains with functional erm gene (inducible macrolide resistance) or 23S rRNA mutations (high-level constitutive resistance) may require continuous/extended IV therapy 1
- Clarithromycin induces erm gene expression more strongly than azithromycin, making azithromycin the preferred macrolide 1
Treatment Duration
- For serious disease, a minimum of 4 months of therapy is necessary 1
- For bone infections, 6 months of therapy is recommended 1
- Complete eradication is uncommon; treatment goals may need to focus on symptomatic improvement and radiographic regression rather than microbiologic cure 1
Surgical Intervention
- Surgery combined with chemotherapy offers the best chance for cure in patients with focal disease who can tolerate lung resection 1
- Surgery is generally indicated for:
- Extensive disease
- Abscess formation
- When drug therapy is difficult 1
Treatment Challenges
- M. abscessus is highly resistant to most antibiotics, with no regimen reliably producing long-term sputum conversion 1
- None of the tested antibiotics show true bactericidal activity against M. abscessus, which may explain poor therapeutic outcomes 5
- For many patients, M. abscessus represents a chronic, incurable infection with current antibiotic options 1
- Suppressive therapy with periodic parenteral antibiotics or oral macrolides may be the most realistic approach for controlling symptoms and disease progression 1
Monitoring
- Regular clinical assessment every 48-72 hours during intensive phase to monitor:
- Fever resolution
- Improvement in symptoms
- Decreasing leukocytosis
- Improved appetite and activity level 6
- Monitor for drug toxicities, particularly with amikacin (ototoxicity, nephrotoxicity) and cefoxitin (neutropenia, thrombocytopenia) 1
The treatment of M. abscessus remains challenging with current antibiotic options, and expert consultation is recommended due to common side effects and toxicities associated with aggressive parenteral therapy 1.