XIFAXAN
Clinical safety rating: caution
Comprehensive clinical and safety monograph for XIFAXAN (XIFAXAN).
Rifaximin is a non-systemic, gut-selective antibiotic that inhibits bacterial RNA synthesis by binding to the beta-subunit of bacterial DNA-dependent RNA polymerase, thereby reducing bacterial overgrowth and altering gut microbiota composition.
| Metabolism | Rifaximin is minimally absorbed (<0.4%) following oral administration; the small absorbed fraction undergoes hepatic metabolism via CYP3A4 and is excreted in feces. It is not significantly metabolized systemically. |
| Excretion | Rifaximin is primarily eliminated unchanged in feces via biliary excretion (approximately 97% of an oral dose). Renal excretion of unchanged drug accounts for <0.4% of the dose. Fecal elimination is the major route. |
| Half-life | The terminal elimination half-life for rifaximin after oral administration ranges from 1.8 to 10 hours, with a mean of approximately 6 hours. The half-life is extended in hepatic impairment due to reduced clearance, and no dosage adjustment is recommended for renal impairment. |
| Protein binding | Rifaximin is highly protein bound (approximately 67-71%) in human plasma, primarily to albumin. Binding is independent of concentration. |
| Volume of Distribution | The apparent volume of distribution (Vd/F) after oral administration ranges from 15 to 60 L (approximately 0.2-0.9 L/kg), with a mean of about 30 L. This relatively low Vd indicates limited extravascular distribution, consistent with its gut-selective action and minimal systemic absorption. |
| Bioavailability | Oral bioavailability is very low, approximately 0.4% due to poor absorption and extensive first-pass metabolism. Systemic absorption is negligible, with rifaximin largely confined to the gastrointestinal tract. |
| Onset of Action | For traveler's diarrhea, clinical response (resolution of loose stools) can be seen within 24-48 hours. For hepatic encephalopathy reduction, onset of reduction in overt HE episodes is typically observed within 7-14 days. Onset of action is dependent on the indication and route (oral only). |
| Duration of Action | Duration of action for treatment of traveler's diarrhea is the course of therapy (3 days). For hepatic encephalopathy prevention, rifaximin is dosed continuously (400 mg twice daily) to maintain remission; the duration of action per dose is approximately 12 hours, supporting twice-daily administration. |
| Molecular Weight | 785.88 |
550 mg orally twice daily for traveler's diarrhea; 550 mg orally three times daily for hepatic encephalopathy.
| Dosage form | TABLET |
| Renal impairment | No dosage adjustment required for renal impairment. Caution in severe renal impairment (CrCl <30 mL/min) due to limited data. |
| Liver impairment | No dosage adjustment recommended for Child-Pugh classes A, B, or C. Monitor for adverse effects in severe hepatic impairment. |
| Pediatric use | Not approved for use in pediatric patients; safety and efficacy not established. |
| Geriatric use | No specific dosage adjustment; use with caution due to potential age-related renal and hepatic function decline. |
| 1st trimester | Insufficient human data; based on animal studies, fetal risk cannot be ruled out. Limited systemic absorption suggests minimal exposure, but caution is advised. |
| 2nd trimester | Insufficient human data; limited systemic absorption may reduce risk, but use only if clearly needed. |
| 3rd trimester | Insufficient human data; limited systemic absorption suggests low risk, but weigh benefits against potential unknown risks. |
Clinical note
Comprehensive clinical and safety monograph for XIFAXAN (XIFAXAN).
| Placental transfer | Based on low oral bioavailability (<0.4%) and high molecular weight, placental transfer is expected to be minimal. However, direct studies are lacking. |
| Breastfeeding | Rifaximin is minimally absorbed orally (<0.4%), and breastmilk levels are likely negligible. However, no published data exist on excretion in human milk. Caution is advised due to lack of safety data in infants. |
■ FDA Black Box Warning
None
| Serious Effects |
Hypersensitivity to rifaximin or any rifamycin antimicrobialBowel obstruction (potential worsening of obstruction)Severe hepatic impairment (Child-Pugh C) - increased systemic exposureDiarrhea with fever or blood in stool (may mask underlying infection)
| Precautions | Hypersensitivity reactions (e.g., angioedema, anaphylaxis), Clostridium difficile-associated diarrhea (CDAD) reported with nearly all antibacterial agents, Use with caution in patients with severe hepatic impairment (Child-Pugh C) due to limited data, Potential for development of bacterial resistance with prolonged use |
| Food/Dietary | No significant food interactions. Can be taken with or without food. Avoid excessive alcohol as it may worsen liver disease in HE patients. No restrictions on any specific foods. |
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| Lactation Rating | L3 (Moderately Safe) |
| Teratogenic Risk | Rifaximin (XIFAXAN) is minimally absorbed orally (<0.4%), resulting in negligible systemic exposure. Animal studies show no evidence of teratogenicity at clinically relevant doses. Human data are limited; however, due to minimal absorption, the risk of fetal harm is considered low across all trimesters. No specific trimester risks have been identified. |
| Fetal Monitoring | No specific maternal or fetal monitoring is required beyond routine prenatal care. Monitor for gastrointestinal effects (e.g., diarrhea) in the mother. |
| Fertility Effects | Animal studies at doses up to 300 mg/kg/day (approximately 120 times the human dose) showed no impairment of fertility. No human data on fertility effects are available; based on minimal systemic absorption, significant impact on fertility is unlikely. |
| Clinical Pearls | XIFAXAN (rifaximin) is a non-absorbable (<0.4%) rifamycin antibiotic, making it ideal for gut-selective therapy. It is FDA-approved for travelers' diarrhea (non-invasive E. coli), irritable bowel syndrome with diarrhea (IBS-D), and hepatic encephalopathy (HE). In IBS-D, use 550 mg three times daily for 14 days; retreatment may be effective if symptoms recur. In HE, 550 mg twice daily is used for maintenance therapy. It does not require dose adjustment in renal or hepatic impairment. Avoid in patients with severe ulcerative colitis due to potential systemic absorption. Note: Rifaximin may cause reddish discoloration of contact lenses or urine (benign). |
| Patient Advice | Take this medication exactly as prescribed for the full course, even if you feel better. · For travelers' diarrhea, start at the first sign of diarrhea; take one 200 mg tablet three times daily for 3 days. · For IBS-D, take two 550 mg tablets three times daily for 14 days; you may repeat if symptoms return. · It may turn your urine or contact lenses reddish-orange; this is harmless. · Do not take with stool softeners or laxatives without consulting your doctor. · Report severe or bloody diarrhea, fever, or worsening symptoms immediately. · Store at room temperature away from moisture and heat. |