Non-Absorbable Antibiotic (Hepatic Encephalopathy / IBS-D) Pregnancy: §4.6: no or limited data in pregnant women; animal studies showed transient effects on ossification and skeletal variations. As a precautionary measure, use during pregnancy is not recommended. Breast-feeding: unknown whether excreted in human milk; a risk to the breast-fed child cannot be excluded.

Rifaximin

Brand names: Targaxan, Xifaxanta

Rifaximin is a minimally absorbed oral antibacterial used in hepatology to reduce the recurrence of overt hepatic encephalopathy and in gastroenterology for certain bowel indications.

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

Frequency: Twice a day

UK SPC (Rifaximin 550 mg film-coated tablets) §4.2: recommended dose 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 patients were using concomitant lactulose. May be administered with or without food; take orally with a glass of water. Elderly: no dosage adjustment necessary. Hepatic impairment: no dosage adjustment necessary, but use with caution in severe (Child-Pugh C) impairment and in patients with a MELD score > 25 (§4.4). Paediatric: safety and efficacy in patients aged less than 18 years have not been established (§4.2) — no paediatric dose stated. Other indications are NOT covered by this UK SPC; US labelling (XIFAXAN, not UK SPC) additionally states travellers' diarrhoea 200 mg three times a day for 3 days and IBS-D 550 mg three times a day for 14 days, retreatable up to twice with the same regimen — verify against UK licensing before use.

Dose adjustments

Renal

§4.2: although a dosing change is not anticipated, caution should be used in patients with impaired renal function. No numeric adjustment stated.

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.

Contraindications

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

Side effects

Peripheral oedema
Nausea
Dizziness
Ascites
Anaemia
Pruritus
Severe cutaneous adverse reactions including Stevens-Johnson syndrome and toxic epidermal necrolysis (frequency not known) — withdraw immediately and never rechallenge

Interactions

Other rifamycin antibacterial agents — no experience of concomitant administration; concomitant use with other rifamycins is not recommended (§4.4/§4.5)
P-glycoprotein inhibitors such as ciclosporin — caution should be exercised when concomitant use is needed (§4.4/§4.5)
Warfarin — both decreases and increases in INR (in some cases with bleeding events) reported; monitor INR carefully on addition or withdrawal of rifaximin and adjust oral anticoagulant dose as needed (§4.4)
In vitro rifaximin did not inhibit major CYP enzymes and was a weak inducer of CYP3A4; in healthy subjects it did not significantly affect the pharmacokinetics of CYP3A4 substrates (§4.5, source text truncated)

Clinical monograph

How it works

It inhibits bacterial RNA synthesis by binding the beta-subunit of bacterial DNA-dependent RNA polymerase; its very low systemic absorption confines activity largely to the gut lumen, reducing ammonia-producing enteric bacteria.

Prescribing in practice

In hepatic encephalopathy it is used to maintain remission and is typically added to lactulose rather than used alone, with treatment reviewed for ongoing benefit.
Although systemic absorption is low, Clostridioides difficile infection has been reported and antibiotic-associated diarrhoea should prompt review.
Caution is advised in severe hepatic impairment, where systemic exposure may increase.

Monitoring

Monitor the frequency and severity of encephalopathy episodes and review for any antibiotic-associated diarrhoea or lack of benefit.

Counselling the patient

Continue any lactulose alongside this medicine unless told otherwise.
Report persistent or severe diarrhoea.
Take regularly as prescribed to help prevent confusion episodes returning.

Evidence & guidelines

Reduction in recurrent hepatic encephalopathy was demonstrated in a landmark randomised trial and the indication is supported by NICE guidance.

Reference: NICE TA337 (rifaximin for HE); Bass et al. NEJM 2010 (RFHE trial); MHRA SPC Targaxan; 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

Pathways