Abstract: We included three RCTs, with 328 participants, that compared six-month regimens with nine-month regimens to treat adults with intestinal and peritoneal TB. All trials were conducted in Asia, and excluded people with HIV, those with co-morbidities and those who had received ATT in the previous five years. Antituberculous regimens were based on isoniazid, rifampicin, pyrazinamide, and ethambutol, and these drugs were administered daily or thrice weekly under a directly observed therapy programme. The median duration of follow-up after completion of treatment was between 12 and 39 months. Relapse was uncommon, with two cases among 140 participants treated for six months, and no events among 129 participants treated for nine months. The small number of participants means we do not know whether or not there is a difference in risk of relapse between the two regimens (very low quality evidence). At the end of therapy, there was probably no difference in the proportion of participants that achieved clinical cure between six-month and nine-month regimens (RR 1.02, 95% CI 0.97 to 1.08; 294 participants, 3 trials, moderate quality evidence). For death, there were 2/150 (1.3%) in the six-month group and 4/144 (2.8%) in the nine-month group. All deaths occurred in the first four months of treatment, so was not linked to the duration of treatment in the included trials. Similarly, the number of participants that defaulted from treatment was small in both groups, and there may be no difference between them (RR 0.50, 95% CI 0.10 to 2.59; 294 participants, 3 trials, low quality evidence). Only one trial reported on adherence to treatment, with only one participant allocated to the nine-month regimen presenting poor adherence to treatment. We do not know whether six-month regimens are associated with fewer people experiencing adverse events that lead to treatment interruption (RR 0.53, 95% CI 0.18 to 1.55; 318 participants, 3 trials, very low quality evidence). We found no evidence to suggest that six-month treatment regimens are inadequate for treating people that have intestinal and peritoneal TB, but numbers are small. We did not find any incremental benefits of nine-month regimens regarding relapse at the end of follow-up, or clinical cure at the end of therapy, but our confidence in the relapse estimate is very low because of size of the trials. Further research is required to make confident conclusions regarding the safety of six-month treatment for people with abdominal TB. Larger studies that include HIV-positive people, with long follow-up for detecting relapse with reliability, would help improve our knowledge around this therapeutic question.

Plain-language summary: Cochrane researchers examined the available evidence up to the 2 September 2016. We included three trials with 328 participants that compared six-month ATT with nine-month ATT; two were from India and one was from South Korea. The trials were mostly of high quality, although two had concerns of risk of bias for detecting relapse of the disease. All the trials included HIV-negative adults with TB of the gut (gastrointestinal TB), and one also included TB of the peritoneum (peritoneal TB). The results show that relapse was an uncommon event, but we are uncertain whether or not there is a difference between the six-month and nine-month groups as numbers of participants are small (very low quality evidence). Six-month and nine-month regimens are probably similarly effective in terms of the chances of achieving cure (moderate quality evidence). Death was uncommon in both groups, and all deaths occurred during the first four months of ATT, which suggests that duration of treatment did not have an effect on risk of death. Few people had poor treatment compliance, and few participants experienced side effects that led to their treatment being stopped or changed, and it was not possible to detect a difference between the groups. Six-month regimens are probably as good as nine-month regimens in terms of numbers of people cured. We found no evidence to suggest that six-month regimens are less safe for gastrointestinal and peritoneal TB than nine-month regimens, but we still do not know whether there is a difference in risk of relapse between the two regimens. Further studies are needed to increase our confidence as to whether six-month regimens are as good as nine-month regimens for preventing relapse; and to provide information about treating abdominal TB in children and in people with HIV.