In a multiple-dose-ranging trial, we previously evaluated higher doses of rifampin in patients for 2 weeks. The objectives of the current study were to administer higher doses of rifampin for a longer period to compare the pharmacokinetics, safety/tolerability, and bacteriological activity of such regimens. In a double-blind, randomized, placebo-controlled, phase II clinical trial, 150 Tanzanian patients with tuberculosis (TB) were randomized to receive either 600 mg (approximately 10 mg/kg of body weight), 900 mg, or 1,200 mg rifampin combined with standard doses of isoniazid, pyrazinamide, and ethambutol administered daily for 2 months. Intensive pharmacokinetic sampling occurred in 63 patients after 6 weeks of treatment, and safety/tolerability was assessed. The bacteriological response was assessed by culture conversion in liquid and solid media. Geometric mean total exposures (area under the concentration-versus-time curve up to 24 h after the dose) were 24.6, 50.8, and 76.1 mg · h/liter in the 600-mg, 900-mg, and 1,200-mg groups, respectively, reflecting a nonlinear increase in exposure with the dose ( P < 0.001). Grade 3 adverse events occurred in only 2 patients in the 600-mg arm, 4 patients in the 900-mg arm, and 5 patients in the 1,200-mg arm. No significant differences in the bacteriological response were observed. Higher daily doses of rifampin (900 and 1,200 mg) resulted in a more than proportional increase in rifampin exposure in plasma and were safe and well tolerated when combined with other first-line anti-TB drugs for 2 months, but they did not result in improved bacteriological responses in patients with pulmonary TB. These findings have warranted evaluation of even higher doses of rifampin in follow-up trials. (This study has been registered at ClinicalTrials.gov under identifier NCT00760149.)

Background: Accumulating data indicate that higher rifampicin doses are more effective and shorten tuberculosis (TB) treatment duration. This study evaluated the safety, tolerability, pharmacokinetics, and 7- and 14-day early bactericidal activity (EBA) of increasing doses of rifampicin. Here we report the results of the final cohorts of PanACEA HIGHRIF1, a dose escalation study in treatment-naive adult smear-positive patients with TB.Methods: Patients received, in consecutive cohorts, 40 or 50 mg·kg⁻¹rifampicin once daily in monotherapy (day 1–7), supplemented with standard dose isoniazid, pyrazinamide and ethambutol between days 8 and 14.Results: In the 40 mg·kg⁻¹cohort (n=15), 13 patients experienced a total of 36 adverse events during monotherapy, resulting in one treatment discontinuation. In the 50 mg·kg⁻¹cohort (n=17), all patients experienced adverse events during monotherapy, 93 in total; 11 patients withdrew or stopped study medication. Adverse events were mostly mild/moderate and tolerability rather than safety related,i.e.gastrointestinal disorders, pruritis, hyperbilirubinaemia and jaundice. There was a more than proportional increase in the rifampicin geometric mean area under the plasma concentration–time curve from time 0 to 12 h (AUC_0–24 h) for 50 mg·kg⁻¹compared with 40 mg·kg⁻¹; 571 (range 320–995)versus387 (range 201–847) mg·L⁻¹·h, while peak exposures saw proportional increases. Protein-unbound exposure after 50 mg·kg⁻¹(11% (range 8–17%)) was comparable with lower rifampicin doses. Rifampicin exposures and bilirubin concentrations were correlated (Spearman's ρ=0.670 on day 3, p<0.001). EBA increased considerably with dose, with the highest seen after 50 mg·kg⁻¹: 14-day EBA −0.427 (95% CI −0.500– −0.355) log₁₀CFU·mL⁻¹·day⁻¹.Conclusion: Although associated with an increased bactericidal effect, the 50 mg·kg⁻¹dose was not well tolerated. Rifampicin at 40 mg·kg⁻¹was well tolerated and therefore selected for evaluation in a phase IIc treatment-shortening trial.

Insight into drug transport mechanisms is highly relevant to the efficacious treatment of tuberculosis (TB). Major problems in TB treatment are related to the transport of antituberculosis (anti-TB) drugs across human and mycobacterial membranes, affecting the concentrations of these drugs systemically and locally. Firstly, transporters located in the intestines, liver, and kidneys all determine the pharmacokinetics and pharmacodynamics of anti-TB drugs, with a high risk of drug-drug interactions in the setting of concurrent use of antimycobacterial, antiretroviral, and antidiabetic agents. Secondly, human efflux transporters limit the penetration of anti-TB drugs into the brain and cerebrospinal fluid, which is especially important in the treatment of TB meningitis. Finally, efflux transporters located in the macrophage and Mycobacterium tuberculosis cell membranes play a pivotal role in the emergence of phenotypic tolerance and drug resistance, respectively. We review the role of efflux transporters in TB drug disposition and evaluate the promise of efflux pump inhibition from a novel holistic perspective.

It is largely unknown if simultaneous administration of tuberculosis (TB) drugs and metformin leads to drug-drug interactions (DDIs). Disposition of metformin is determined by organic cation transporters (OCTs) and multidrug and toxin extrusion proteins (MATEs). Thus, any DDIs would primarily be mediated via these transporters. This study aimed to assess the in vitro inhibitory effects of TB drugs (rifampin, isoniazid, pyrazinamide, ethambutol, amikacin, moxifloxacin, and linezolid) on metformin transport and whether TB drugs are also substrates themselves of OCTs and MATEs. HEK293 cells overexpressing OCT1, OCT2, OCT3, MATE1, and MATE2K were used to study TB drug-mediated inhibition of [ ¹⁴ C]metformin uptake and to test if TB drugs are transporter substrates. Metformin uptake was determined by quantifying [ ¹⁴ C]metformin radioactivity, and TB drug uptake was analyzed using liquid chromatography-tandem mass spectrometry. DDI indices were calculated (plasma maximum concentrations [ C _max ]/50% inhibitory concentrations [IC ₅₀ ]), and based on the literature, a cutoff of >0.1 was assumed to warrant further in vivo investigation. Moxifloxacin was the only TB drug identified as a potent inhibitor (DDI index of >0.1) of MATE1- and MATE2K-mediated metformin transport, with IC ₅₀ s of 12 μM (95% confidence intervals [CI], 5.1 to 29 μM) and 7.6 μM (95% CI, 0.2 to 242 μM), respectively. Of all TB drugs, only ethambutol appeared to be a substrate of OCT1, OCT2, OCT3, MATE1, and MATE2K. MATE1-mediated ethambutol uptake was inhibited strongly (DDI index of >0.1) by moxifloxacin (IC ₅₀ , 12 μM [95% CI, 3.4 to 43 μM]). Our findings provide a mechanistic basis for DDI predictions concerning ethambutol. According to international guidelines, an in vivo interaction study is warranted for the observed in vitro interaction between ethambutol and moxifloxacin.