IC50: RNA polymerase

Rifalazil exhibits antimicrobal activity against Gram-positive enteric bacteria, inhibits Clostridium difficile , Clostridium perfringens , Bacteroides fragilis with MIC ₅₀ value of 0.0015, 0.0039, 0.0313 μg/ml, respectively. Rifalazil exhibits antimicrobal activity against Gram-negative enteric bacteria, inhibits Escherichia coli and Klebsiella pneumoniae with MIC ₅₀ value of 16 and 16 μg/ml, respectively. 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 MIC ₅₀ value of 0.0078, 0.0078, 0.0078, 0.0078, 0.0002, 0.0001 μg/ml, respectively. Rifalazil exhibits antimicrobal activity against Helicobacter pylori , Chlamydia pneumoniae and Chlamydia trachomatis with MIC ₅₀ value of 0.004, 0.000125 and 0.00025 μg/ml, respectively.

Rifalazil (oral gavage; 20, 25, and 150 mg/kg; 6-8 weeks) combines with isoniazid (INH) 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. And the addition of Pyrazinamide (PZA) does not significantly improve RLZ-INH therapy at any time point.