Rifamycins By Brian J Werth, PharmD, University of Washington School of Pharmacy Reviewed / Revised May 2022 | Modified Sep 2022 View Patient Education Rifabutin, Rifampin, and Rifapentine Pharmacokinetics Indications Contraindications Use During Pregnancy and Breastfeeding Adverse Effects Dosing Considerations Rifaximin More Information Topic Resources Mechanisms of Action: Nucleic... The rifamycins are bactericidal antibiotics; they inhibit bacterial DNA-dependent RNA polymerase, suppressing RNA synthesis.