What is the recommended treatment regimen for Mycobacterium terrae infections?

Treatment of Mycobacterium terrae Infections

For Mycobacterium terrae infections, the recommended treatment regimen consists of a macrolide (clarithromycin or azithromycin) plus ethambutol, with consideration of adding a third drug such as rifampicin or sulfamethoxazole, for a duration of at least 12 months after clinical response.

Understanding M. terrae

Mycobacterium terrae is a nontuberculous mycobacterium (NTM) that can cause clinical disease in both immunocompetent and immunocompromised hosts. While specific guidelines for M. terrae are limited, treatment approaches can be derived from guidelines for other similar NTM species.

Treatment Approach

Initial Assessment

• Determine the site and extent of infection (pulmonary vs. extrapulmonary)
• Obtain drug susceptibility testing when possible
• Evaluate patient's immune status and comorbidities

Recommended Regimen

For Pulmonary Disease:

• First-line therapy:
  • Clarithromycin 500 mg twice daily or azithromycin 250-500 mg daily
  • Ethambutol 15 mg/kg daily
  • Consider adding rifampicin 600 mg daily as a third agent

For Extrapulmonary Disease (especially tenosynovitis):

• First-line therapy:
  • Clarithromycin 500 mg twice daily or azithromycin 250-500 mg daily
  • Ethambutol 15 mg/kg daily
  • Sulfamethoxazole or rifampicin as a third agent 1, 2
  • Consider surgical debridement for localized disease

Duration of Treatment

• Continue treatment for at least 12 months after clinical response or culture conversion 2
• For severe or recalcitrant cases, longer treatment durations may be necessary

Evidence and Rationale

The British Thoracic Society (BTS) guidelines for management of NTM pulmonary disease recommend multidrug regimens for similar NTM species 3. While M. terrae is not specifically addressed in most guidelines, the approach to treatment follows principles established for treating other NTM infections.

Case reports have demonstrated successful treatment of M. terrae infections using:

• A 6-month regimen of clarithromycin and sulfamethoxazole for knee infection 1
• Macrolide-based regimens plus ethambutol and a third effective drug for at least 12 months after clinical response 2

Special Considerations

Tenosynovitis

M. terrae commonly causes tenosynovitis of the upper extremity (59% of reported cases), often following trauma 2. Treatment may require:

• Combined medical and surgical approach
• Prolonged antibiotic therapy
• Possible repeated debridement in refractory cases

Monitoring During Treatment

• Monthly clinical assessment
• Monitor for drug toxicities:
  • Ethambutol: Visual acuity and color discrimination
  • Macrolides: Hepatic function, QT interval
  • Rifampicin: Hepatic function
• For pulmonary disease: Sputum cultures every 1-3 months to assess response

Treatment Challenges

• M. terrae infections can be difficult to treat, with approximately 50% of tenosynovitis cases requiring repeated debridement, tendon extirpation, or amputation despite antibiotic therapy 2
• Consider parenteral aminoglycoside therapy in severe or refractory cases

Alternative Approaches

For patients who cannot tolerate first-line agents, consider:

• Fluoroquinolones (moxifloxacin)
• Linezolid
• Clofazimine
• Aminoglycosides for severe disease

Conclusion

Treatment of M. terrae infections requires a prolonged course of multiple antibiotics. The cornerstone of therapy includes a macrolide plus ethambutol, with consideration of a third agent based on the site and severity of infection. Surgical intervention may be necessary for localized disease, particularly tenosynovitis.