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 resistant 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. Mechanism of action
Rifaximin interferes with transcription by binding to the β-subunit of bacterial RNA polymerase. This results in the blockage of the translocation step that normally follows the formation of the first phosphodiester bond, which occurs in the transcription process. This in turn results in a reduction of bacteria populations, including gas-producing bacteria, which may reduce mucosal inflammation, epithelial dysfunction, and visceral hypersensitivity. Rifaximin has broad spectrum antibacterial properties against both gram positive and gram negative anaerobic and aerobic bacteria. As a result of bile acid solubility, its antibacterial action is limited mostly to the small intestine and less so the colon. A resetting of the bacterial composition has also been suggested as a possible mechanism of action for relief of IBS symptoms. Additionally, rifaximin may have a direct anti-inflammatory effect on gut mucosa via modulation of the pregnane X receptor. Other mechanisms for its therapeutic properties include inhibition of bacterial translocation across the epithelial lining of the intestine, inhibition of adherence of bacteria to the epithelial cells, and a reduction in the expression of proinflammatory cytokines.
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). Special caution
Patients should avoid Rifaximin usage if they are allergic to Rifabutin, Rifampin and Rifapentine. It may cause attenuated vaccines (such as typhoid vaccine) to not work well. Health care professionals should be informed about its usage before having any immunizations. Pregnant or breastfeeding women should avoid taking it as it is a pregnancy category C drug and can harm the foetus. Cautious use is required in individuals with cirrhosis of the liver who have a Child-Pugh score of class C severity. 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 the drug. There were no deaths while using it in the clinical trials.The most common side effects includes 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:

Clostridium difficile-associated diarrhea (CDAD)
Drug-resistant bacterial superinfection
Severe allergic reactions including hives, rashes and itching

Interactions
As Rifaximin is not significantly absorbed from the gut, the great majority of these drug interactions are negligible in people with healthy liver function, so healthcare providers usually do not worry about drug interactions unless liver impairment is present. It may decrease the effectiveness of warfarin, a commonly prescribed anticoagulant, in people with liver problems.