Safety and Efficacy of High Dose Rifampicin in Tuberculosis (TB)-HIV Co-infected Patients on Efavirenz- or Dolutegravir-based Antiretroviral Therapy

Overview

Higher doses of rifampicin has been associated with a faster drop in bacterial load over time, and shorter treatment regimens with high dose rifampicin are being proposed. Sub-therapeutic rifampicin concentrations are common in TB patients and have been demonstrated in several studies carried out among patients with tuberculosis receiving the standard dose (10mg/kg) of rifampicin. Insufficient exposure to isoniazid and rifampicin, which are the cornerstones of TB treatment, has been associated with drug resistance, treatment failure and delayed bacterial clearance from sputum. Evidence has indicated that the current dose of rifampicin (10mg/kg) is inadequate for many patients. Several studies have suggested that dose escalation (to 20-35mg/kg) is safe, and that higher doses (35mg/kg) may accelerate clearance of TB bacteria from the sputum of infected individuals and achievement of target concentrations.15,16 However, these studies have almost entirely been conducted among HIV negative TB patients, or TB-HIV co-infected patients without severe immunosuppression who are not yet receiving antiretroviral therapy (ART). TB-HIV co-infected patients on multiple additional drugs, including ART, are at increased risk of drug-drug interactions and drug related toxicities, including hepatotoxicity. Increasing the dose of rifampicin is a promising approach; however, there is paucity of data on the safety of higher doses of rifampicin in HIV infected patients on ART, and almost no information on the enzyme induction effect of high dose rifampicin on Efavirenz (EFV) and Dolutegravir (DTG). In this study, the investigators will not only evaluate for the enzyme induction effect of 35mg/kg of rifampicin on the most widely used first-line antiretrovirals, but will also look at the safety of these combinations in a population in which there is still scarce safety data. The aim of this study is to determine the safety of higher doses of rifampicin and its effect on the pharmacokinetics of efavirenz and dolutegravir in TB-HIV co-infected patients.

The investigators will enroll 120 TB-HIV co-infected patients initiating TB treatment. Participants will be randomized to either high dose (35mg/kg) or standard dose (10mg/kg) rifampicin in addition to either dolutegravir (DTG) or efavirenz (EFV), for those who are antiretroviral therapy (ART) naïve. Patients who are already on ART will remain on their current ART regimen. The randomization groups (30 participants in each arm) include:Arm One A: R35mg/kg Isoniazid/Ethambutol/Pyrazinamide (HEZ) + DTG, Arm One B: R10mg/kg HEZ + DTG (Control 1), Arm Two A: R35mg/kg HEZ + EFV, Arm Two B: R10mg/kg HEZ + EFV (Control 2). High dose rifampicin will be administered for the first 8 weeks (intensive phase) of TB treatment. All other anti-TB drugs will be administered at the standard dose using fixed-dose combinations (FDC). All participants will receive standard dose rifampicin during the continuation phase (weeks 9 -24). Pharmacokinetic (PK) blood sampling will be performed after 6 weeks (±2 weeks) of TB treatment. PK sampling will occur pre-dose and at 1, 2, 4 and 8 hours after observed dose for rifampicin and DTG concentrations and approximately 12-14 hours post-dose for EFV (to measure mid-dose interval (MDI) concentration). The EFV MDI and rifampicin pre-dose samples will be collected concurrently in the EFV arms. Safety laboratory tests including liver and renal function tests will be measured every two weeks or when patients present with symptoms suggestive of toxicity. In participants with culture positive TB at baseline, sputum cultures will be performed after 8 weeks of anti-TB treatment. The investigators will use population pharmacokinetic modelling to determine the rifampicin and DTG exposure in each arm. Using these models the investigators will evaluate for drug-drug interactions between ART and the standard and high dose of rifampicin. Investigators will compare the mid-dose concentrations of EFV and trough concentrations of DTG in each intervention and control arm using Wilcoxon rank-sum test. The investigators will also compare the proportion of participants with grade 3 or 4 adverse events in each arm using the chi-squared test. Investigators will compare the proportion of participants who are sputum culture negative after 8 weeks of treatment among those in the high dose and standard dose arms using the chi-squared test.