Fixed-dose combination associated with faster time to smear conversion compared to separate tablets of anti-tuberculosis drugs in patients with poorly controlled diabetes and pulmonary tuberculosis in Qatar

BACKGROUND: Diabetes is associated with increased risk of tuberculosis (TB) treatment failure, death, and relapse compared to patients without diabetes. Current TB regimens are available as fixed dose combination (FDC) and separate tablets (ST), in which using the former is purported to make it easier to adhere and complete treatment. So far there are no studies assessing the performance of FDC compared to ST in diabetic patients with pulmonary TB. METHODOLOGY: A retrospective cohort study was conducted, and included eight hospitals in Qatar in which patients diagnosed with pulmonary TB received rifampin, isoniazid, pyrazinamide, and ethambutol (as FDC or ST) given as directly observed therapy. Sputum smears for acid fast bacilli were tested weekly. We included patients admitted between December 2012 and December 2015, ≥18 years old, diagnosed with TB with pretreatment positive sputum smears, and having diabetes. Patients with Mycobacterium tuberculosis that was resistant to any first-line drug were excluded. Blood glucose was monitored closely and controlled to < 180 md/dL using oral hypoglycemic agents and/or insulin. We assessed the effectiveness of TB regimens by comparing time to confirmed negative smears between those treated with FDC or ST, and the impact of adding metformin. RESULTS: 103 patients met inclusion criteria. Mean age and body mass index were 45.6 ± 9.1 years and 22.1 ± 3.6 kg/m(2), respectively. Fifty-four (52%) patients received the FDC. There was no difference between groups in baseline characteristics and sputum bacillary loads. Patients prescribed FDC showed faster times to sputum smear conversion compared to ST (32 ± 19 vs. 46 ± 31 days, p = 0.01). The difference was greater among patients with pretreatment bacillary load of 3+ (FDC 36.6 ± 19.5 vs. ST 56.1 ± 28.8, p = 0.008). Receipt of metformin≥2000 mg/day altered the difference in time to smear conversion (FDC 30.7 ± 13.4 vs. ST 62 ± 35.5, p = 0.016), which was of greatest difference in those with pretreatment bacillary load 3+ and who received metformin≥2000 mg/day (FDC 36 ± 12.1 vs. ST 92.2 ± 26 days, p = 0.001). CONCLUSION: Patients with diabetes and prescribed FDC showed faster smear conversion during treatment for pulmonary TB compared to ST which was more pronounced in those with 3+ bacillary load pretreatment and which appeared to be modified by higher dose metformin.