Antibiotic Pregnancy: There is no or limited data from use in pregnant women and animal studies showed transient effects on ossification and skeletal variations in the foetus — as a precautionary measure, use during pregnancy is not recommended. It is unknown whether rifaximin/metabolites are excreted in human milk and a risk to the breast-fed child cannot be excluded — decide whether to discontinue breast-feeding or to discontinue/abstain from therapy. Animal studies do not indicate harmful effects on male or female fertility.

Rifaximin

Brand names: Targaxan, Xifaxan

Rifaximin is a gut-selective antibiotic used to reduce the recurrence of overt hepatic encephalopathy, usually alongside lactulose, and is also used for travellers' diarrhoea.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: 550 mg

Route: Oral — orally with a glass of water; can be administered with or without food

Frequency: Twice a day

Recommended dose is 550 mg twice a day as long term treatment for the reduction in recurrence of episodes of overt hepatic encephalopathy. In the pivotal study, 91% of the patients were using concomitant lactulose. Elderly: no dosage adjustment is necessary. Hepatic impairment: no dosage adjustment is necessary for patients with hepatic insufficiency, but use with caution in severe (Child-Pugh C) hepatic impairment and in patients with a MELD score greater than 25 (SPC 4.4). Paediatric population: the safety and efficacy of rifaximin 550 mg in patients aged less than 18 years have not been established. INDICATION SCOPE: this UK SPC (rifaximin 550 mg film-coated tablets) covers hepatic encephalopathy only — it states no posology for travellers diarrhoea, IBS-D or small intestinal bacterial overgrowth; source those separately if the page covers them. Safety: rifaximin must be withdrawn immediately if signs or symptoms of severe cutaneous adverse reactions (SJS/TEN) appear, and must never be restarted in that patient.

Dose adjustments

Renal

Although a dosing change is not anticipated, caution should be used in patients with impaired renal function.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

US labelling (FDA)

Reference — US labelling, may differ from UK

Condition Recommended Oral Dosage TD ( 2.1 ) 200 mg 3 times a day for 3 days HE ( 2.2 ) 550 mg 2 times a day IBS-D ( 2.3 ) 550 mg 3 times a day for 14 days. Patients who experience recurrence can be retreated up to 2 times with the same regimen. XIFAXAN can be taken with or without food. ( 2.4 ) 2.1 Dosage for Travelers’ Diarrhea The recommended dosage of XIFAXAN is 200 mg taken orally three times a day for 3 days. 2.2 Dosage for Hepatic Encephalopathy The recommended dosage of XIFAXAN is 550 mg taken orally two times a day. 2.3 Dosage for Irritable Bowel Syndrome with Diarrhea The recommended dosage of XIFAXAN is 550 mg taken orally three times a day for 14 days. Patients who experience a …

Source: US FDA prescribing information (openFDA / DailyMed), label dated 2025-08-27. Accessed 2026-06-12. US dosing and indications can differ from UK practice — use UK sources for prescribing decisions.

Contraindications

Hypersensitivity to rifaximin, rifamycin-derivatives or to any of the excipients
Cases of intestinal obstruction

Side effects

Peripheral oedema (15.0% vs 8.2% on placebo in study RFHE3001)
Nausea (14.3%)
Dizziness (12.9%)
Ascites (11.4%)
Muscle spasms and pruritus (9.3% each); anaemia (7.9%)
Severe cutaneous adverse reactions including Stevens-Johnson syndrome and toxic epidermal necrolysis, which can be life-threatening or fatal (frequency unknown)

Interactions

Other rifamycins — concomitant administration is not recommended due to lack of data and the potential for severe disruption of gut flora with unknown consequences; there is no experience of giving rifaximin to subjects taking another rifamycin antibacterial for a systemic infection
P-glycoprotein inhibitors such as ciclosporin — caution should be exercised when concomitant use is needed
Warfarin — both decreases and increases in INR (in some cases with bleeding events) have been reported; if co-administration is necessary, monitor INR carefully on addition or withdrawal of rifaximin and adjust the oral anticoagulant dose as needed
CYP enzymes — in vitro, rifaximin did not inhibit the major CYP drug metabolising enzymes and did not induce CYP1A2 or CYP2B6, but was a weak inducer of CYP3A4; in healthy subjects it did not significantly affect the pharmacokinetics of CYP3A4 substrates (effect in hepatically impaired patients less certain)

Clinical monograph

How it works

It is a minimally absorbed, broad-spectrum antibacterial that inhibits bacterial RNA synthesis, acting largely within the gut lumen to reduce ammonia-producing enteric bacteria.

Prescribing in practice

For hepatic encephalopathy it is used to maintain remission and is normally added to, rather than replacing, lactulose.
Because systemic absorption is minimal, systemic adverse effects and drug interactions are few and it is generally well tolerated.
Clostridioides difficile infection has been reported rarely, so consider this if severe or persistent diarrhoea develops.

Monitoring

No specific routine monitoring is required for the encephalopathy indication; assess clinical response and tolerability and continue lactulose as indicated.

Counselling the patient

For hepatic encephalopathy, keep taking your lactulose as well unless told otherwise.
Report severe, persistent or bloody diarrhoea rather than treating it yourself.

Evidence & guidelines

Recommended to reduce recurrence of hepatic encephalopathy (NICE TA337).

Reference: SONIC Trial Lancet 2010; NICE NG215 Cirrhosis; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Drugs

Co-amoxiclav · Antibiotic

Pathways