Rifalazil is a rifamycin derivative, inhibits the bacterial DNA-dependent RNA polymerase and kills bacterial cells by blocking off the β-subunit in RNA polymerase. Rifalazil is an antibiotic, exhibits high potency against mycobacteria, gram-positive bacteria, Helicobacter pylori, C. pneumoniae and C. trachomatis (MIC: 0.00025 to 0.0025 μg/ml).

Rifalazil exhibits antimicrobal activity against Gram-positive enteric bacteria, inhibits Clostridium difficile, Clostridium perfringens, Bacteroides fragilis with MIC50 value of 0.0015, 0.0039, 0.0313 μg/ml, respectively[3]. Rifalazil exhibits antimicrobal activity against Gram-negative enteric bacteria, inhibits Escherichia coli and Klebsiella pneumoniae with MIC50 value of 16 and 16 μg/ml, respectively[3]. Rifalazil exhibits antimicrobal activity against non-enteric Gram-positive bacteria, inhibits Methicillin-susceptible Staphylococcus aureus, Methicillin-resistant S. aureus, Methicillin- and quinolone-resistant S. aureus, Staphylococcus epidermidis, Streptococcus pyogenes, Streptococcus pneumoniae with MIC50 value of 0.0078, 0.0078, 0.0078, 0.0078, 0.0002, 0.0001 μg/ml, respectively[3]. Rifalazil exhibits antimicrobal activity against Helicobacter pylori, Chlamydia pneumoniae and Chlamydia trachomatis with MIC50 value of 0.004, 0.000125 and 0.00025 μg/ml, respectively[3].

Rifalazil (p.o.; 20, 25, and 150 mg/kg; 6-8 weeks) combines with isoniazid for 6 weeks or greater significantly reduced the number of mice per group in which?M. tuberculosis?is detected in both spleens and lungs compared to the reductions for the early and late controls [2].