Rifaximin

Rifaximin, sold under the brand name Xifaxan among others, is a non-absorbable, broad-spectrum antibiotic mainly used to treat travelers' diarrhea. It is based on the rifamycin antibiotics family. Since its approval in Italy in 1987, it has been licensed in more than 30 countries for the treatment of a variety of non-infectious gastrointestinal diseases like irritable bowel syndrome and hepatic encephalopathy. It acts by inhibiting RNA synthesis in susceptible bacteria by binding to the RNA polymerase enzyme. This binding blocks translocation, which stops transcription. It was developed by Salix Pharmaceuticals.

Medical uses

Travelers' diarrhea Rifaximin is used to treat travelers' diarrhea caused by E. coli bacteria in people aged twelve years of age and older. It treats travelers' diarrhea by stopping the growth of the bacteria that cause diarrhea. Rifaximin will not work to treat travelers' diarrhea that is bloody or occurs with fever.

Irritable bowel syndrome Rifaximin is used for the treatment of irritable bowel syndrome (IBS). It possesses anti-inflammatory and antibacterial properties, and is a non-absorbable antibiotic that acts locally in the gut. These properties make it efficacious in relieving chronic functional symptoms of non-constipation type irritable bowel syndrome. It appears to retain its therapeutic properties for this indication, even after repeated courses. It is particularly indicated where small intestine bacterial overgrowth is suspected of involvement in irritable bowel syndrome. Symptom relief or improvement can be obtained for global irritable bowel syndrome symptoms, including: abdominal pain, flatulence, bloating, and stool consistency. A drawback is that repeated courses may be necessary for remission of symptoms.

Clostridioides difficile infection Rifaximin may also be a useful addition to vancomycin when treating people with relapsing C. difficile infection. However, the quality of evidence of these studies was judged to be low. Because exposure to rifamycins in the past may increase risk for resistance, rifaximin should be avoided in such cases.

Hepatic encephalopathy Rifaximin is used to prevent episodes of hepatic encephalopathy (changes in thinking, behavior, and personality caused by a build-up of toxins in the brain in adults who have liver disease). It treats hepatic encephalopathy by stopping the growth of bacteria that produce toxins and that may worsen the liver disease. Although high-quality evidence is lacking, it appears to be as effective as, or more effective than, other available treatments for hepatic encephalopathy (such as lactulose), is better tolerated, and may work faster. It prevents reoccurring encephalopathy and is associated with high patient satisfaction. People are more compliant and satisfied to take this medication than any other due to minimal side effects, prolonged remission, and overall cost. The drawbacks are increased cost, and lack of robust clinical trials for hepatic encephalopathy without combination lactulose therapy.

Other uses Other uses include treatment of: infectious diarrhea, small intestinal bacterial overgrowth, inflammatory bowel disease, and diverticular disease. It is effective in treating small intestinal bacterial overgrowth regardless of whether it is associated with irritable bowel syndrome or not. It has also shown efficacy with rosacea, ocular rosacea which also presents as dry eyes for patients with co-occurrence with small intestinal bacterial overgrowth (SIBO).

Veterinary uses Rifaximin is used to treat cattle mastitis intramammarily and post-partum metritis intrauterinally.

Contraindications People should avoid rifaximin if they are allergic to either rifabutin, rifampin, or rifapentine. It may cause attenuated vaccines (such as typhoid vaccine) not to work well. Health-care professionals should be informed about its usage before giving immunizations. Pregnant or breastfeeding women should avoid rifaximin: it can harm the fetus. Caution is required in people with cirrhosis who have a Child–Pugh score of C.

Side effects Rifaximin has an excellent safety profile due to its lack of systemic absorption. Clinical trials did not show any serious adverse events while using rifaximin. There were no deaths while using it in the clinical trials. The most common side effects include nausea, stomach pain, dizziness, fatigue, headaches, muscle tightening, and joint pain. It may also cause reddish discoloration of urine. The most serious side effects of rifaximin are:

Clostridioides difficile-associated diarrhea Drug-resistant bacterial superinfection Severe allergic reactions including hives, rashes and itching

Interactions Rifaximin has been found to be a CYP3A4 inducer in vitro. However, as rifaximin is not significantly absorbed from the gut, the great majority of this drug's interactions are negligible in people with healthy liver function, so healthcare providers usually do not worry about drug interactions unless liver impairment is present. Accordingly, rifaximin showed no influence on the pharmacokinetics of the CYP3A4 substrate midazolam in clinical studies. Rifaximin may decrease the effectiveness of warfarin, a commonly prescribed anticoagulant, in people with liver problems.

Pharmacology Rifaximin is a semisynthetic broad spectrum antibacterial drug, derived through chemical modification of the natural antibiotic rifamycin. It has very low bioavailability due to its poor absorption after oral administration. Because of this local action within the gut and the lack of horizontal transfer of resistance genes, the development of bacterial resistance is rare, and most of the drug taken orally stays in the gastrointestinal tract where the infection takes place. Rifaximin has been found to increase abundance of butyrate-producing bacteria such as Faecalibacterium prausnitzii in animals and humans.

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