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Rifaximin (Xifaxan)

Antibioticprescriptionoral · inferred

Non-absorbable (less than 0.4% systemic absorption) rifamycin-class antibiotic that acts locally in the gut by inhibiting bacterial DNA-dependent RNA polymerase. Approved for traveler's diarrhea (E. coli, 200 mg TID for 3 days), hepatic encephalopathy prevention in cirrhosis (550 mg BID maintenance), and IBS-D (550 mg TID for 14 days with re-treatment for recurrence). Because systemic absorption is negligible, the typical mass-in-body PK framework does not predict efficacy, therapeutic activity is entirely lumenal/mucosal. Plasma t1/2 ~6h of the tiny fraction absorbed. F<0.004. Drug interactions are minimal; rare pseudomembranous colitis and hypersensitivity. Minimal CYP induction despite being a rifamycin.

Projected serum levels — 550 mg, twice daily

Rifaximin (Xifaxan)
Rifaximin (Xifaxan) modeled serum levels, 550 mg twice daily over 15 days Population-based pharmacokinetic estimate. Steady state reached after approximately 7 days. 0 0.25 0.50 0.75 1 Day 0 Day 4 Day 7 Day 11 Day 15 Time on a regular schedule ≈ steady state · day 7

Maintenance schedule: 550 mg twice daily (oral).

Modeled steady state after ~7 days: peak ≈ 0 mg, trough ≈ 0 mg body load. Population-based estimate over 15 days for a 550 mg dose at a 70 kg reference body mass — the interactive app scales curves to your doses, timing, and body mass.

Key facts

Category
Antibiotic
Route modeled
Oral
Model confidence
inferred
Common dose
550 mg
Suggested maximum
1.6k mg/day
Reference dose range
275–1.6k mg (single dose)
Suggested cadence
twice daily

Documented interactions

  • moderate
    Carvedilol (Coreg) + Rifaximin (Xifaxan) Transporter inhibition

    Carvedilol (Coreg) inhibitor of P-gp may alter Rifaximin (Xifaxan) absorption / distribution

  • moderate
    CBD (Cannabidiol) + Rifaximin (Xifaxan) Transporter inhibition

    CBD (Cannabidiol) inhibitor of P-gp may alter Rifaximin (Xifaxan) absorption / distribution

  • moderate
    Efavirenz (Sustiva) + Rifaximin (Xifaxan) Transporter induction

    Efavirenz (Sustiva) inducer of P-gp may alter Rifaximin (Xifaxan) absorption / distribution

  • moderate
    Fisetin + Rifaximin (Xifaxan) Transporter inhibition

    Fisetin inhibitor of P-gp may alter Rifaximin (Xifaxan) absorption / distribution

  • moderate
    Ginkgo Biloba (EGb 761) + Rifaximin (Xifaxan) Transporter inhibition

    Ginkgo Biloba (EGb 761) inhibitor of P-gp may alter Rifaximin (Xifaxan) absorption / distribution

  • moderate
    Panax Ginseng (Asian Ginseng) + Rifaximin (Xifaxan) Transporter induction

    Panax Ginseng (Asian Ginseng) inducer of P-gp may alter Rifaximin (Xifaxan) absorption / distribution

Serum checks 17 modeled interaction pairings for rifaximin (xifaxan) across your whole stack — absorption conflicts, enzyme inhibition, and nutrient depletion included.

Research behind this entry

  1. Rifaximin: a novel nonabsorbed rifamycin for gastrointestinal disorders Scarpignato C, Pelosini I · Chemotherapy, 2005 DOI

    Pharmacology review: rifaximin <0.4% systemically absorbed, delivers high lumenal concentrations throughout GI tract, broad gram+/gram-/anaerobic coverage with low resistance emergence.

  2. Rifaximin treatment in hepatic encephalopathy Bass NM et al. · New England Journal of Medicine, 2010 DOI

    Pivotal 299-patient RCT: rifaximin 550 mg BID reduced recurrence of overt hepatic encephalopathy by 58% vs placebo and hospitalization involving HE by 50% over 6 months.

2 published studies referenced in the app, each with a plain-language summary.