Rifaximin

Absorption

Low absorption in both the fasting state and when administered within 30 minutes of a high-fat breakfast.

Toxicity

LD50 > 2 g/kg (orally, in rats)

Description

Rifaximin is an antibiotic structurally related to rifamycin. It is reported to be efficacious in the treatment of gastrointestinal infections and hepatic encephalopathy, being highly active against Gram-positive and -negative aerobic and anaerobic bacteria. Due to poor systemic absorption, rifaximin is effective in presurgical sterilization of the GI tract.It displays good activity against a wide spectrum of bacteria, including Salmonella spp., S. aureus, and E. coli.

The Uses of Rifaximin

Rifaximin is a non-absorbable semisynthetic Rifamycin antibiotic.

What are the applications of Application

Rifaximin is a Pregnane X receptor agonist and antibiotic that inhibits RNA synthesis and activates PXR.

Background

Rifaximin is a semisynthetic, rifamycin-based non-systemic antibiotic, meaning that the drug will not pass the gastrointestinal wall into the circulation as is common for other types of orally administered antibiotics. It has multiple indications and is used in treatment of traveller's diarrhea caused by E. coli; reduction in risk of overt hepatic encephalopathy recurrence; as well as diarrhea-predominant irritable bowel syndrome (IBS-D) in adult women and men. It is marketed under the brand name Xifaxan by Salix Pharmaceuticals.

Indications

Rifaximin has multiple indications by the FDA: for the treatment of patients (≥12 years of age) with traveller's diarrhea caused by noninvasive strains of Escherichia coli; for the reduction of overt hepatic encephalopathy recurrence in patients ≥18 years of age; and in May 2015 it was approved for irritable bowel syndrome with diarrhea (IBS-D) treatment in adult men and women.

Pharmacokinetics

Rifaximin is a structural analog of rifampin and a non-systemic, gastrointestinal site-specific antibiotic. This non-systemic property of the drug is due to the addition of a pyridoimidazole ring, which renders it non-absorbable. Rifaximin acts by inhibiting bacterial ribonucleic acid (RNA) synthesis and contributes to restore intestinal microflora imbalance. Other studies have also shown rifaximin to be an pregnane X receptor (PXR) activator. As PXR is responsible for inhibiting the proinflammatory transcription factor NF-kappa B (NF-κB) and is inhibited in inflammatory bowel disease (IBD), rifaximin was proven to be effective for the treatment of IBS-D.

Metabolism

In vitro drug interactions studies have shown that rifaximin, at concentrations ranging from 2 to 200 ng/mL, did not inhibit human hepatic cytochrome P450 isoenzymes: 1A2, 2A6, 2B6, 2C9, 2C19, 2D6, 2E1, and 3A4. In an in vitro hepa-tocyte induction model, rifaximin was shown to induce cytochrome P450 3A4 (CYP3A4), an isoenzyme which rifampin is known to induce.