Rifamycin SV is a derivative of antibiotic rifamycin B (the natural fermentation product of S. mediterranei broths). The primary target of rifampicin on whole bacteria is the synthesis of RNA. Rifamycin belongs to the ansamycin class of antibacterial drugs and acts by inhibiting the beta subunit of the bacterial DNA-dependent RNA polymerase, blocking one of the steps in DNA transcription. This results in inhibition of bacterial synthesis and consequently growth of bacteria. Rifampicin exhibits bactericidal activity on Gram-positive and Gram-negative bacteria and on mycobacteria. Rifamycin SV MMX® (AEMCOLO), a non-absorbable rifamycin antibiotic formulated using the multi-matrix system, was designed to exhibit its pharmacological action on the distal small intestine and colon. AEMCOLO is indicated for the treatment of travelers’ diarrhea (TD) caused by non-invasive strains of Escherichia coli in adults.

Rifaximin is a structural analog of rifampin and a non-systemic, gastrointestinal site-specific antibiotic. Rifaximin acts by inhibiting bacterial ribonucleic acid (RNA) synthesis and contributes to restore intestinal microflora imbalance. It is FDA approved for the treatment of travelers’ diarrhea, reduction in risk of overt hepatic encephalopathy (HE) recurrence and treatment of irritable bowel syndrome with diarrhea. More common side effects are: black, tarry stools; dizziness or lightheadedness; muscle spasm; rapid breathing; shortness of breath; trouble sleeping. Co-administration of cyclosporine, with XIFAXAN resulted in 83-fold and 124-fold increases in rifaximin mean Cmax in healthy subjects.

Rifalazil (also known as KRM-1648) is a derivative of the antibiotic rifamycin. This orally administered ansamycin is under evaluation for treatment of various bacterial infections. Rifalazil kills bacterial cells by blocking off the β-subunit in RNA polymerase. This drug was originally developed as a therapeutic agent to replace rifampin in the treatment of tuberculosis. It also showed potential to treat indications caused by chlamydia trachomatis and chlamydia pneumoniae. Furthermore, it has been suggested as a potential drug in the treatment of gastric ulcer disease (which is caused by Helicobacter pylori) and antibiotic-associated colitis. Phase II studies evaluated the efficacy and safety of this drug in patients with chlamydia trachomatis and chlamydia seropositive patients. A phase 3 study was initiated including chlamydia seropositive patients. However, the development of rifalazil was terminated in 2013 due to severe side effects.