In the sixth edition of its guide (see publications on this site), The Union proposes thus a slighlty different approach in the cascade of regimens than the World Helath Organization (WHO). The first line regimen is now concordant with the six-month regimen recommended by WHO. If sputum smears are positive at the mandatory 5-month examination and molecular tests to confirm or exclude multidrug-resistant tuberculosis arre not available, it is recommended that the patients be treated again with first-line drugs, but for 8 months, and adding streptomycin during the intensive phase.
The rationale for this recommendation is that the majority of patients with positive smears at five months will not have multidrug resistance, but will have positive smears either because adherence was poor, non-viable bacilli stain, or isoniazid mono-resistance slowed down converison.
If the reason for positive smears is poor adherence, the propsoed regimen should be successful if adherence can now be assured.
If the bacilli are non-viable, the regimen will also be successful.
If the strain is resistant to isoniazid alone, the 5-drug combination during the intensive phase shoud successfully overcome it.
If there is true multidrug resistance, streptomycin might be lost, but of little impact as the multidrug resistance regimen switches to the use of other injectable drugs. There is a risk of also loosing ethambutol which is potentially useful (and is used) in a regimen for multidrug resistance, but the risk of acuisition of ethambutol resistance is reduced by limiting it to the intensive phase. Loosing pyrazinamide is of lesser concern as this drugs acts only in an acid milieu which contains a small number of bacilli and the probability of selecting resistant mutants is thus small. That this is the case has been demonstrated in that patients with multidrug-resistant tuberculosis who also received pyrazinamide have strains that are still susceptible to the drug. |
