Effect of Metformin on Plasma Exposure of Rifampicin, Isoniazid, and Pyrazinamide in Patients on Treatment for Pulmonary Tuberculosis

Background: To evaluate the effect of metformin on the plasma levels of rifampicin, isoniazid, and pyrazinamide in patients with drug-sensitive pulmonary tuberculosis being treated with first-line antituberculosis treatment (ATT) and to assess the influence of gene polymorphisms on the metabolic pathway of metformin and plasma levels of antitubercular drugs. Methods: Nondiabetic adults aged 18–60 years with pulmonary tuberculosis were randomized to either the standard ATT (ATT group) or ATT plus metformin (METRIF group) groups in a phase IIB clinical trial. An intensive pharmacokinetic study with blood collection at 0 hour (predosing), followed by 1, 2, 4, 6, 8, and 12 hours after dosing was conducted during the first month of treatment in a subset of 60 study participants after a minimum of 14 doses. Plasma concentrations of rifampicin, isoniazid, pyrazinamide, and metformin were measured by high-performance liquid chromatography using validated methods, and pharmacokinetic parameters and OCT1 and MATE1 gene polymorphisms were compared between the groups. Results: Significant increases in the clearance of rifampicin, isoniazid, and pyrazinamide were observed in patients in the METRIF group (n = 29) compared with those in the ATT group (n = 31). The AA genotypes of the single-nucleotide polymorphism of rs2289669 (MATE1) in the METRIF group showed a significantly decreased area under the concentration–time curve to the last observation point and increased clearance of rifampicin. Conclusions: Metformin altered rifampicin and isoniazid plasma concentrations in patients receiving antituberculosis treatment for pulmonary tuberculosis with little effect on sputum conversion at the end of treatment. Studies with larger sample sizes are needed to understand host drug–drug interactions.