bBedaquiline is a newly approved drug for the treatment of multidrug-resistant tuberculosis, but there are concerns about its safety in humans. We found that the coadministration of verapamil with subinhibitory doses of bedaquiline gave the same bactericidal effect in mice as did the full human bioequivalent bedaquiline dosing. Adding verapamil to bedaquiline monotherapy also protected against the development of resistant mutants in vivo. The adjunctive use of verapamil may permit use of lower doses of bedaquiline to be used and thereby reduce its dose-related toxicities in tuberculosis patients.
Bedaquiline (also known as Sirturo, TMC-207, R207910, or the "J" compound) represents the first novel drug class to be approved by the U.S. Food and Drug Administration in the last 40 years for the treatment of multidrug-resistant tuberculosis (MDR-TB) (1, 2). The recommended human dosage of bedaquiline is 400 mg once daily for the first 2 weeks, followed by 200 mg three times per week from weeks 3 to 24 (3). Bedaquiline usage in patients presents several safety concerns, including increased mortality and liver-related adverse drug reactions. Bedaquiline also prolongs the QT interval in patients, which is a measure of the time between the start of the Q wave and the end of the T wave in the electrical cycle of the heart. In a phase II trial involving patients with advanced MDR-TB, a significantly higher number of participants receiving bedaquiline died than those receiving a placebo, although the causes of mortality were not directly attributable to the drug (4, 5). Thus, strategies to reduce the human dose of bedaquiline while retaining antibacterial activity may be valuable.The active efflux of drugs is known to play a major role in antimicrobial resistance in Mycobacterium tuberculosis (6). Smallmolecule inhibition of efflux pumps improves the activity of several antimycobacterial agents that are subject to efflux. Verapamil is an efflux pump inhibitor that has been shown to have an antimicrobial-potentiating effect in the treatment of M. tuberculosis both in vitro and in vivo (7). Recently, it was shown that inhibition of the efflux pumps of M. tuberculosis by verapamil reduces the bacterial drug tolerance induced in the intracellular compartment within macrophages and in zebrafish granuloma-like lesions (8). The addition of verapamil to standard TB treatment accelerates both the bactericidal and the sterilizing activities of the regimen in a mouse model (9).We recently showed that supplementing bedaquiline with verapamil profoundly decreases the MIC of bedaquiline in the wildtype strain M. tuberculosis H37Rv and also in drug-susceptible and drug-resistant clinical isolates. The MIC of clofazimine against M. tuberculosis H37Rv also decreased significantly in the presence of 50 g/ml verapamil (10). We hypothesized that these results may extend to an in vivo infection model and that verapamil may potentiate the killing of M. tuberculosis by bedaquiline and accelerate the clearance of mycobacteria. Shortening treatment...