Emergence of Extensively Resistant Tuberculosis

Tuberculosis is usually treated with ‘first-line’ anti-tuberculous drugs’ such as isoniazid, rifampin, ethambutol, and pyrazinamide.

Multi-drug resistant tuberculosis (MDR) is disease due to strains resistant to both isoniazid and rifampicin. Treatment of such strains requires use of ‘second-line’ drugs which include fluoroquinolones, aminoglycosides, capreomycin (injectable drugs), para-aminosalicylate, cycloserine, and ethionamide.

Recently, however, strains resistant to fluoroquinolones have been noticed worldwide. When MDR TB strains become resistant to fluoroquinolones, treatment becomes difficult since other drugs used have limited efficacy. Treatment options become even more limited when in addition to fluoroquinolones, strains are resistant to any one of the injectable drugs. Such strains are labeled extensively drug resistant (XDR).

Patients with XDR TB require longer duration of treatment (at least 18 months) with drugs regimens that incorporate both old and new agents. Newer drugs for optimal treatment of XDR TB need to be discovered.

XDR TB has recently been reported from Pakistan. Hasan et al (IJID 2009)have reported 22 XDR cases seen from 1997 to 2007. Appropriate treatment of all tuberculosis patients would help prevent further rise in XDR rates.