Rifaximin is an oral, non-systemic antibiotic belonging to the rifamycin class. It is marketed in pill form and is available in strengths of 200 mg and 400 mg. In Hong Kong, rifaximin is a prescription-only medication regulated by the Hong Kong Department of Health under the Pharmacy and Poisons Ordinance. Several manufacturers supply rifaximin tablets, but the active ingredient is the same across brands.
Rifaximin remains largely confined to the gastrointestinal (GI) tract because it is poorly absorbed (< 0.5 % of the dose enters systemic circulation). It exerts its antibacterial effect by binding to the β-subunit of bacterial DNA-dependent RNA polymerase, thereby blocking bacterial RNA synthesis and halting protein production. This mechanism reduces the total bacterial load in the gut without causing significant systemic exposure, which limits many typical antibiotic-related side effects.
Key pharmacologic points
Rifaximin has received regulatory approval in Hong Kong for the following indications:
These uses are supported by clinical trials that demonstrated symptom improvement and reduction in hepatic encephalopathy episodes when rifaximin is added to standard care.
Small Intestinal Bacterial Overgrowth (SIBO) - Several open-label studies and systematic reviews suggest that rifaximin can reduce bacterial overgrowth and improve bloating and abdominal discomfort in SIBO. While promising, this indication is not approved by the Hong Kong regulatory authorities.
Off-label use requires medical supervision and individualized risk assessment.
These effects are usually transient and resolve without intervention.
The exact regimen, duration, and need for repeat courses depend on the condition being treated and should be set by a qualified healthcare professional.
This article provides educational information about rifaximin and is not a substitute for professional medical advice. Treatment decisions, including use for unapproved indications, must be made under the guidance of a qualified healthcare provider. The content is intended for informational purposes and does not constitute medical recommendations. Always consult a physician before starting, stopping, or changing any medication regimen.
Yes, rifaximin is commonly prescribed for the prevention and treatment of traveler’s diarrhea caused by non-invasive E. coli. It is taken before or during travel as directed by a clinician, typically for a short 3-day course.
Take the missed tablet as soon as you remember unless it is almost time for the next scheduled dose. In that case, skip the missed dose and resume your regular schedule; do not double the dose.
Rifaximin’s activity is limited to the gut, so it may reduce both pathogenic and beneficial bacteria. Some clinicians advise pausing probiotics during treatment and restarting them after the course ends, but there is no strict contraindication.
Rifaximin is approved for secondary prevention of hepatic encephalopathy in patients with liver cirrhosis. Because it is minimally absorbed, it is generally well-tolerated, but liver enzymes should be monitored periodically.
Rifaximin does not typically appear on standard occupational or sports drug-screening panels because it is not systemically absorbed in measurable amounts.
The standard regimen for IBS-D involves a 14-day treatment course. Longer or repeated courses should only be considered under medical supervision.
Inactive components may include lactose, microcrystalline cellulose, and magnesium stearate, but exact formulations can vary between manufacturers. Check the patient information leaflet for specifics.
Rifaximin has limited activity against C. difficile and is not recommended for primary treatment of C. difficile infection. In some cases, it has been studied as an adjunct to prevent recurrence, but this remains off-label.
There is no direct interaction between rifaximin and alcohol. However, excessive alcohol consumption can worsen liver disease and hepatic encephalopathy, conditions for which rifaximin may be prescribed.
Rifaximin is a non-systemic, gut-restricted rifamycin, whereas ciprofloxacin is a systemic fluoroquinolone that distributes throughout the body and carries a broader spectrum of side effects. This confinement reduces systemic toxicity but limits its use to gastrointestinal indications.
