Rifaximin

Rifaximin is an antibiotic that fights intestinal bacterial infection. It is used to treat traveler's diarrhea caused by the bacterium Escherichia coli. Infection occurs after consuming contaminated foods or liquids.

Rifaximin is sold under the name Xifaxan by Salix Pharmaceuticals. The Food and Drug Administration approved its use on May 25, 2004.

Scanning electron micrograph (SEM) of rod-shaped Escherichia coli bacteria. Magnification 3607x. Source: Wikimedia Commons

Other Names

Rifaximin is sold under two other brand names in Europe:

• Spiraxin
• Zaxine

Uses

Rifaximin is used for the treatment of traveler's diarrhea caused by noninvasive strains of Escherichia coli in patients older than 12 years of age.

Rifaximin is also used for the treatment of hepatic encephalopathy. When used to treat this condition, it is considered to be an "orphan drug," which is one that is used for diseases that affect only a small number of people.

How Rifaximin is Taken

Rifaximin is taken by mouth. For traveler's diarrhea, the recommended dose is a 200-mg tablet taken three times a day for three straight days.

How Rifaximin Works

Rifaximin is in the family of rifamycin antibiotics. It binds to the ribonucleic acid (RNA) polymerase enzyme in bacteria. Bacteria need RNA to grow, and this binding prevents the bacteria from making more RNA.

How the Body Affects Rifaximin

Absorption of rifaximin into the bloodstream is low. Studies have demonstrated that 80% to 90% of rifaximin taken by mouth concentrates in the gut. This accumulation enhances the effectiveness of rifaximin in the treatment of intestinal infections.

Due to its distribution in the gut, rifaximin is excreted almost entirely in the feces. The half-life, or time needed for the concentration of rifaximin in the blood to be reduced by half, is approximately six hours.

Side Effects

Post-marketing studies of rifaximin have shown that the most common side effects are allergic reactions. Some of the reactions are listed below:

• inflammationof the skin (exfoliative dermatitis)
• rash
• swelling of face and tongue and difficulty swallowing (angioneurotic edema)
• hives
• flushing
• itching

These side effects can occur within 15 minutes of taking the drug.

Risks and Precautions

Rifaximin is discontinued if diarrhea symptoms get worse, or persist for more than 24–48 hours. If this occurs, treatment with another antibiotic is usually considered.

Treatment with antibiotics like rifaximin alters the normal bacterial make-up of the colon and may permit overgrowth of the bacterium Clostridium difficile. Studies indicate that a toxin produced by these bacteria is the primary cause of pseudomembranous colitis. Pseudomembranous colitis is inflammation in regions of the colon that causes irritation and bleeding. It ranges in severity from mild to life-threatening. Mild cases of pseudomembranous colitis usually respond to drug discontinuation alone. In moderate to severe cases, treatment with an antibiotic effective against Clostridium difficile is generally given.

The influence of rifaximin on the fetus is not known. Rifaximin is only used in pregnancy if the potential benefit outweighs the potential risk. Similarly, breast-feeding mothers should be aware of the potential risk of transmitting the drug to an infant through breast milk.

Rifaximin is not used in patients who are allergic to rifampin (Rifadin) because it is structurally similar to rifampin and has caused skin reactions in sensitive patients.

Drug Interactions

To date, no interactions with other drugs that are modified by enzymes in the liver have been reported.

Research

The effectiveness of rifaximin was evaluated in two studies involving patients with traveler's diarrhea. The first study was conducted at clinical sites in Mexico, Guatemala, and Kenya. The second study was conducted in Mexico, Guatemala, Peru, and India.^[1]

Both studies showed that the duration of diarrhea was significantly shorter in patients treated with rifaximin than in the placebo group. More rifaximin-treated patients were classified as clinical cures than were those in the placebo group.

The second study further demonstrated that patients with fever and/or blood in the stool who were treated with Xifaxanhad lower clinical cure rates than those without fever or blood in the stool. Many of the patients with fever and/or blood in the stool had invasive pathogens other than E. coli, such as Campylobacter jejuni. This finding indicated that rifaximin is effective for treatment of intestinal infections involving E. coli, but not for systemic infections that may involve other strains of bacteria.

Alternatives

Depending on the severity of the symptoms, there are several alternatives for the treatment of traveler's diarrhea:

• Anti-motility agents: These agents, which include loperamide (Imodium), medications containing diphenoxylate (Lomotil), and opiates (such as paregoric and codeine), provide temporary relief from diarrhea by slowing the transit time through the digestive system and allowing more time for absorption.

• Bismuth subsalicylate (Pepto-Bismol): Pepto-Bismol can decrease the frequency of the stools and shorten the duration of the illness.

• Other antibiotics: These include trimethoprim-sulfamethoxazole (Bactrim DS), doxycycline (Vibramycin), and ciprofloxacin (Cipro).

References

1. ↑ Steffen R, Sack DA, Riopel L, et al. Therapy of traveler's diarrhea with rifaximin on various continents. Am J Gastroenterol 2003;98:1073-8. Abstract

External Links

FDA: Xifaxan

Rx List: Xifaxan

Drugs.com: Xifaxan