10% (25/249)

5% (11/229)

Sputum negative, Still being followed

81% (201/249)

90% (205/229)

Lost to Follow-up

9% (23/249)

6% (13/229)

• All data through 8 July 1997 for patients with confirmed susceptible MTB (rifapentine combination, n=286; rifampin combination, n=284).

Risk of relapse was higher in the rifapentine regimen. During the Intensive Phase of treatment the rate of noncompliance with companion medications was somewhat higher for the rifapentine regimen than for the rifampin regimen. Most of the relapses occurred among those with poor compliance with these companion medications and this group also had the largest risk of relapse for the rifapentine regimen relative to the rifampin regimen. This factor appears to explain most, but not all, of the higher relapse rate observed in the rifapentine arm. Failure to convert sputum after two months of treatment (e., end of Intensive Phase) was associated with a greater risk of relapse for both treatment regimens. Relapse rates were also higher for males in both regimens. Relapse in the rifapentine group was not associated with development of mono-resistance to rifampin.

In vitro susceptibility testing was conducted against initial and subsequent M.tuberculosis isolates recovered from 620 patients enrolled in the study. Rifapentine and rifampin MIC values were determined employed the radiometric susceptibility testing method utilizing 7H 12 broth at pH 6.8 (NCCLS procedure M24.T). Six hundred and fourteen patients with rifampin susceptible (MIC ≤ 0.5m g/mL) strains of M. tuberculosis had rifapentine MICs of ≤ 0.125 m g/mL. The remaining six patients with rifampin resistant (MIC > 8.0 m g/mL). M.tuberculosis isolates had rifapentine MICs of >8.0 m g/mL. Four of these represented baseline values for patients with multiresistant tuberculosis. One rifampin resistant isolate was from a rifapentine relapse patient while the remaining isolate was from a rifampin relapse patient. Restriction fragment length polymorphism (RFLP) studies showed the rifapentine relapse isolate to be genetically different from the baseline strain while RFLP data on the matched rifampin isolate is pending. This information is provided for comparative purpose only as rifapentine breakpoints have not been established.

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