Effect of six- versus eight-month regimen on treatment success and smear conversion among retreatment patients

Background: In 2017, the regimen for patients with retreatment
tuberculosis (TB) changed from an eight-month treatment regimen that
consisted of Isoniazid, Rifampicin, Pyrazinamide, Ethambutol, and
Streptomycin (2RHZES/1RHZE/5RHE) to a six-month treatment regimen
(2RHZE/4RH). Currently, there is uncertainty regarding the effect of the
six-month treatment regimen on treatment outcomes across TB Control
Programs. We evaluated the effect of the six-month treatment regimen on
treatment success rate (TSR) and sputum smear conversion (SSC) among
patients with retreatment pulmonary bacteriologically confirmed TB
(PBC-TB) in Kampala, Uganda. Methods: Between November 2021 and February
2022, we abstracted data for patients with retreatment PBC-TB who had
received treatment between January 2012 and July 2021 across six large TB
clinics in Kampala, Uganda. The primary outcome was TSR defined as cure or
treatment completed. The secondary outcome was SSC defined as a change in
sputum smear test result from positive to negative. We applied
doubly-robust regression estimation for causal effect analysis, with TSR
as the primary outcome and SSC at 2/3, 5, and 6/8 months as secondary
outcomes. We reported average causal effects using marginal odds ratios
(MOR) and 95% confidence intervals (CI). Results: We analyzed data for 427
participants with an overall mean age of 34.6±10.8 years. Over half
(53.9%) of the participants were treated with a six-month treatment
regimen. TSR was 49.6% overall, and higher in the six-month regimen group
(52.2%) than in the eight-month regimen group (46.7%). The six-month
treatment regimen significantly improved the TSR compared to the
eight-month treatment regimen (MOR, 1.27; 95% CI, 1.06-1.52). However, the
effect of the six-month treatment regimen on SSC at (MOR, 1.01; 95% CI,
0.91-1.12), 5 months (MOR, 0.96; 95% CI, 0.88-1.04), and 6/8 months (MOR,
0.83; 95% CI, 0.19-3.51) is similar to the eight-month treatment regimen.
Conclusion: The six-month treatment regimen results in a better TSR among
patients with retreatment PBC-TB compared to the eight-month treatment
regimen. Therefore, patients with retreatment PBC- TB who do not have
rifampicin resistance should continue to receive the six-month treatment
regimen.