This study assessed the safety, tolerability, and pharmacokinetic interaction between PA-824, a novel antitubercular nitroimidazo-oxazine, and midazolam, a CYP3A4 substrate, in 14 healthy adult male and female subjects. The study followed up on observations in vitro that PA-824 caused weak and time-dependent inhibition of CYP3A4. Subjects received a single oral dose of midazolam (2 mg), followed by a 2-day washout. After the washout, all subjects received PA-824 (400 mg) once daily for 14 consecutive days. On day 14, all subjects received the final PA-824 dose coadministered with a 2-mg oral dose of midazolam. The pharmacokinetic endpoints AUC 0 -t , AUC 0 -ؕ , and C max for midazolam and 1-hydroxy midazolam were compared between midazolam administered alone versus midazolam coadministered with PA-824. Statistical analysis demonstrated that the mean midazolam values of C max , AUC 0 -t , and AUC 0 -ؕ parameters were reduced by ca. 16, 15, and 15%, respectively, when PA-824 was coadministered with midazolam. The total exposure (AUC) of 1-hydroxy midazolam was 13 to 14% greater when coadministered with PA-824 compared to midazolam administered alone. The C max of 1-hydroxy midazolam was similar between treatments. Based on these results, PA-824 does not inhibit or induce CYP3A4 to a clinically meaningful extent and is not likely to markedly affect the pharmacokinetics of CYP3A4 metabolized drugs.
PA-824 is an antitubercular nitroimidazo-oxazine that possesses significant activity against replicating and nonreplicating/persistent Mycobacterium tuberculosis via a complex mechanism of action distinct from that of any currently marketed drugs for the treatment of tuberculosis (1, 2). Its mechanism of action is believed similar to that of Delamanid, a drug currently under review for market approval by the regulatory authorities (3). PA-824 interferes with M. tuberculosis cell wall biosynthesis by inhibiting the oxidation of hydroxymycolate to ketomycolate. A deazaflavin (F420)-dependent nitroreductase has also been identified whose activity in M. tuberculosis cells is involved in PA-824 activation and activity (2). Reduction of PA-824 to its des-nitroimidazole metabolite by this nitroreductase is associated with generation of reactive nitrogen species, including nitric oxide. PA-824 is active against M. tuberculosis isolates resistant to single or multiple antituberculous drugs and has proven effective in shortening treatment time of drug-sensitive M. tuberculosis in a murine model of tuberculosis (TB) as part of novel drug regimens (4). Moreover, PA-824 was highly active as monotherapy in a 14-day dose ranging early bactericidal activity (EBA) study in humans where similar efficacy profiles were observed across all doses assessed (200 to 1,200 mg/day) (5). In EBA studies, the rate of change over time in the number of M. tuberculosis CFU per ml of sputum in an overnight sputum collection is used to compare different dosing and treatment regimens. In a follow up study exploring a lower dose range (50 to 200 mg/day), a d...