Xifaxan (rifaximin)

Rifaximin, a structural analog of rifampin, is a rifamycin antibiotic.

Rifaximin is a semisynthetic derivative of rifampin. Like other rifamycins, rifaximin inhibits RNA synthesis in susceptible bacteria by binding to the beta subunit of bacterial DNA-dependent RNA polymerase.

Due to limited and variable systemic absorption, rifaximin is not suitable for the treatment of systemic bacterial infections. Rifaximin systemic exposure is dose-proportional over a dosage range of 200-400 mg, and systemic exposure is less than dose-proportional over a dosage range of 400-600 mg. Following oral administration of rifaximin (single or multiple doses of 550 mg) in healthy individuals, mean peak plasma concentrations are attained about 1 hour after dosing and range from 2.4-4 ng/mL.

In patients treated with oral rifaximin (200 mg three times daily for 3 days), plasma concentrations and systemic exposure (area under the plasma concentration-time curve (AUC)) are low and variable and accumulation of the drug does not occur. In patients with a history of hepatic encephalopathy receiving rifaximin (550 mg twice daily), the mean AUC of rifaximin is approximately 12-fold higher than that reported in healthy individuals. In patients with irritable bowel syndrome (IBS) with diarrhea receiving rifaximin (550 mg three times daily for 14 days), the time to peak plasma concentrations, mean peak plasma concentrations, and AUC of rifaximin are similar to those reported in healthy individuals.

When rifaximin was administered 30 minutes after a high-fat meal in healthy individuals, peak plasma concentrations of the drug were not affected; however, the time to peak plasma concentrations was delayed from 0.75 to 1.5 hours after the dose and AUC was increased twofold. Rifaximin is moderately bound to human plasma proteins (67.5 or 62% in healthy individuals or patients with hepatic impairment, respectively). Systemically absorbed rifaximin undergoes extensive metabolism, principally by cytochrome P-450 (CYP) isoenzyme 3A4.

Following a 400-mg oral dose of rifaximin, 96.6% of the dose is excreted in feces (mostly as unchanged drug) and 0.3% is excreted in urine (mostly as metabolites). The mean half-life of rifaximin at steady-state is 5.6 hours in healthy individuals and 6 hours in patients with IBS with diarrhea.

Rifaximin is active in vitro and in clinical infections (i.e., infectious diarrhea) against most isolates of enterotoxigenic Escherichia coli (ETEC) and enteroaggregative Escherichia coli (EAEC).

Rifaximin should not be used to treat diarrhea accompanied by fever or blood in the stool, or due to pathogens other than E. coli. Do not use rifaximin in patients where Campylobacter jejuni (C. jejuni), Shigella, and Salmonella are suspected as causative organisms. Rifaximin is not effective against C. jejuni, and has not been proven effective against Shigella and Salmonella.

When selecting or modifying anti-infective therapy, results of culture and in vitro susceptibility testing should be used. In the absence of such data, local epidemiology and susceptibility patterns should be considered when selecting anti-infectives for empiric therapy.

Resistance to rifaximin generally is associated with mutations in the rpoB gene that change the binding site on DNA-dependent RNA polymerase and decrease rifaximin binding affinity. Cross-resistance between rifaximin and other classes of anti-infectives has not been observed.

USES: This medication is used to treat diarrhea caused by the common bacteria known as E. coli ("traveler's diarrhea"). Rifaximin should not be used if you have a fever or bloody diarrhea. It works by stopping the growth of bacteria.

This antibiotic treats only bacterial infections. It will not work for viral infections (such as common cold, flu). Using any antibiotic when it is not needed can cause it to not work for future infections.

Rifaximin is also used to treat irritable bowel syndrome with diarrhea. It is also used to prevent a brain problem caused by liver disease (hepatic encephalopathy).

Generic name: rifaximin
Pronunciation: (rif-AX-i-min)

The following indications are listed for Xifaxan:

• Diarrhea Predominant Irritable Bowel Syndrome
• Hepatic Encephalopathy
• Traveler's Diarrhea Due To Noninvasive Strain Of Escherichia Coli

Also known as: Diarrhea Predominant Ibs, Diarrhea Predominant Spastic Colon, Portal Systemic Encephalopathy, Traveler's Diarrhea Due To Noninvasive E. Coli.

No ICD codes are available for this drug.