Drug-resistance encountered in the retreatment of Mycobacterium tuberculosis infections

Patients who had prior anti-tuberculosis medications for pulmonary tuberculosis and who return to the hospital with culture-positive tuberculosis have been considered to be at risk of harboring resistant bacilli (secondary resistance or acquired resistance). The present recommendation for therapy of these patients is to resume earlier anti-tuberculosis medications and to add two new agents until the drug susceptibilities of the bacilli are known. This study reviewed 112 cases of readmissions for active tuberculosis and evaluated the risk of acquired drug resistance in this group. Patients with 6 months or less of prior therapy rarely harbored resistant organisms. Patients with 6-12 months of prior therapy had an 88% possibility of harboring resistant bacilli, but only a 30% risk of harboring multiple-drug resistant bacilli. Patients with 12 months or more of prior therapy had a 66% risk of harboring multiple-drug resistant, difficult-to-treat bacilli. This data would indicate that only those patients who have had prior therapy for 7 months or more require aggressive initial readmission therapy with 4 or more anti-tuberculosis agents. Hopefully this finding will not only help clinicians to identify readmission tuberculosis patients who are at increased risk of harboring resistant organisms but will also help them to be more selective in prescribing aggressive, potentially toxic, multiple-drug regimens.