Activity of nitazoxanide and tizoxanide against Mycobacterium tuberculosis in vitro and in whole blood culture

Nitazoxanide (NTZ) and its metabolite tizoxanide (TIZ) were studied as antimycobacterial agents in vitro (in mycobacterial growth indicator tube [MGIT] cultures) and in a whole blood bactericidal assay. Both NTZ and TIZ show high protein binding. In MGIT cultures (albumin concentration = 78 μM), inhibition of Mycobacterium tuberculosis growth occurred at total drug concentrations of ≥16 μg/ml, whereas in whole blood cultures (albumin concentration = 350 μM), ≥128 μg/ml was required. Free drug fractions at these two conditions were estimated to be 69% and 2%, respectively. Co-incubation of NTZ and TIZ in human plasma for 72 h nearly completely eliminated their ability to inhibit mycobacterial growth in MGIT. Interactions with plasma proteins may limit the potential of NTZ and TIZ as drugs for human tuberculosis.