Rifamycin (structural analogue of rifampin)
Escherichia coli, Clostridium difficile
Rifamycins bind to and inhibit DNA-dependant RNA polymerase
Most likely concentration-dependant killing (peak/MIC and AUC/MIC)
Cmax (fasting): 0.004 mcg/L; Tmax: 1.2 ± 0.5 hours; Half-life: 5.8 ± 4.3 hours; AUC: 0.018 (mcg*h/mL)
* Note: Rifaximin should NOT be used for systemic infection since less than 0.4% is absorbed after oral administration
CNS: headache was seen with both rifaximin and placebo in clinical trials
Allergic: hypersensitivity reactions, allergic dermatitis, and angioneurotic edema have been described uncommonly
PO: 200 mg tablets
For Traveler’s diarrhea: 200mg tablet PO q8h
Not FDA approved for patients < 12 years of age
Hepatic failures: No change in dosing, due to limited systemic absorption
Renal failures: Not studied in this population. No change expected due to limited systemic absorption
NOT effective in patients with Traveler’s diarrhea due to Campylobacter jejuni, and unproven when caused by Shigella spp. and Salmonella spp.
Rifaximin should be discontinued if diarrhea persists or worsens over 24 to 48 hours
Rifamixin, like other rifamycins, is an inducer of CYP3A4 isoenzymes. Little effect is expected, due to limited systemic absorption
Limited drug-drug interaction studies have shown the following:
Midazolam: No difference in midazolam systemic exposure when coadministered either IV or PO with rifaximin.
Oral contraception: Single dose studies have been conducted with rifaximin and 0.07 ethinyl estradiol and 0.5mg norgestimate, and showed that the kinetics of the oral contraceptive were not altered.
Category C: Risk unknown. Human studies inadequate.
Efficacy: Resolution of diarrhea in Traveler’s diarrhea
Xifaxan - Salix Pharmaceuticals, USA
Dermodis – Farmades, Italy
Flonorm - Schering-Plough, Mexico
Normix - Alfa Wassermann, Czech Republic, Hungary, Italy
Rifacol - Prodotti Formenti, Italy, Germany
Spiraxin - Bama, Spain
Zaxine - Cantabria, Spain