Rifaximin

Rifaximin is a non-absorbable antibiotic of the rifamycin class used to treat several gastrointestinal conditions. It acts locally in the gut by inhibiting bacterial RNA synthesis through binding to bacterial DNA-dependent RNA polymerase, which reduces transcription in susceptible organisms. Because it is poorly absorbed from the gastrointestinal tract, systemic exposure is minimal and most of the drug remains in the intestinal lumen.

Common indications include traveler's diarrhea caused by noninvasive strains of Escherichia coli, reducing the risk of overt hepatic encephalopathy in adults with cirrhosis, and treatment of irritable bowel syndrome with diarrhea (IBS-D) in adults. Dosing varies by indication: for traveler's diarrhea, a typical regimen is 200 mg taken orally three times daily for 3 days; for IBS-D, 550 mg three times daily for about 14 days; for hepatic encephalopathy, 550 mg three times daily is commonly used, with regimens tailored to the patient’s history and guidelines.

Pharmacokinetics are characterized by minimal systemic absorption; the majority of the dose is excreted in feces, and plasma concentrations remain very low. Consequently, drug interactions are limited, though patients should inform clinicians of all medications and supplements.

Adverse effects are generally mild and mainly GI-related, such as nausea, flatulence, and abdominal discomfort, with occasional headaches or elevated liver enzymes. Serious hypersensitivity is rare. Antibiotic treatment can disrupt gut flora and, as with other antibiotics, carries a small risk of Clostridioides difficile infection.

Contraindications include hypersensitivity to rifaximin or other rifamycin derivatives. Safety in pregnancy and lactation is not well established; use only if potential benefits justify risks and discuss with a healthcare provider.