Antibiotic Pregnancy: C — animal studies show teratogenicity; avoid if possible

Rifaximin

Brand names: Targaxan, Xifaxan

Adult dose

Dose: Hepatic encephalopathy (secondary prevention): 550mg BD. Traveller's diarrhoea: 200mg TDS × 3 days

Route: Oral

Frequency: Twice daily (HE); three times daily (traveller's diarrhoea)

Max: 1.1g/day (HE)

HE (NICE NG215): add to lactulose for secondary prevention of overt HE. Traveller's diarrhoea: non-invasive E. coli only — not for febrile diarrhoea, bloody diarrhoea, or Campylobacter.

Dose adjustments

Renal

No adjustment required — minimal systemic absorption (<0.4%).

Hepatic

Use in hepatic impairment is the primary indication — no dose adjustment needed.

Clinical pearls

SONIC trial: rifaximin 550mg BD + lactulose reduced overt HE recurrence at 6 months by 58% vs lactulose alone (NNT = 4).
NHS England Commissioning: rifaximin is recommended for secondary prevention of overt HE after 2 or more episodes — prior authorisation may be needed.
Minimal systemic absorption (< 0.4%) — gut-selective antibiotic. Modifies gut microbiome rather than eliminating all enteric bacteria.
Urine discolouration (orange/red): warn patients — rifamycin class effect, not haematuria.

Contraindications

Intestinal obstruction
Hypersensitivity to rifamycin antibiotics

Side effects

GI disturbance (nausea, abdominal pain) — generally mild
Headache
Orange discolouration of urine (harmless — rifamycin class)

Interactions

P-glycoprotein substrates: minimal systemic absorption makes interactions unlikely
Warfarin: theoretical reduction in warfarin effect with rifamycins (rare at low systemic levels)

Monitoring

Symptoms of HE
stool frequency/consistency
ammonia level (HE monitoring)

Reference: SONIC Trial Lancet 2010; NICE NG215 Cirrhosis; NICE BNF 84. Verify against your local formulary and the latest BNF before prescribing.

Curated clinical cross-links plus same-class fallbacks.

Calculators

Drugs

Co-amoxiclav · Antibiotic

Pathways