Two recent studies examined the clinical use of the antimicrobial rifaximin. Rifaximin is a minimally absorbed antimicrobial drug, blocks bacterial RNA polymerase, is highly concentrated in the gastrointestinal tract, and demonstrates broad-spectrum antimicrobial coverage. Studies have suggested that most of the administered drug is excreted in the feces and that chronic inflammatory conditions do not result in increased absorption. It has an excellent safety profile with few adverse effects and has been used in surgical prophylaxis, a variety of gastrointestinal conditions, and hepatic encephalopathy. Treatment for this condition is primarily performed to reduce nitrogenous wastes in the intestine through the use of oral antibiotics and lactulose; many of the commonly used antibiotics result in severe side effects.

In the first study, 299 patients in hepatic encephalopathy remission from chronic liver disease were randomly assigned to receive rifaximin (n = 140) or placebo (n = 159) for 6 months. Clinical efficacy was determined by the initial breakthrough episode of hepatic encephalopathy as the first endpoint and hospitalization as the second endpoint; breakthrough hepatic encephalopathy occurred in 22.1% of rifaximin recipients vs 45.9% of controls, and hospitalization occurred in 13.6% and 22.6%, respectively. In this population, rifaximin prolonged hepatic encephalopathy remission and decreased instances of hospitalization for the condition. The second study evaluated efficacy of rifaximin treatment in 23 children with inflammatory bowel disease. Children presented with abdominal pain, diarrhea, and bloody stools and were accordingly treated with rifaximin. Clinical symptoms of each condition were relieved with rifaximin therapy, and relief increased over time. Sixty-one percent of the population had clinical relief, and rifaximin was the primary therapeutic addition.

Commentary: Inflammatory bowel disease and hepatic encephalopathy are common clinical conditions in companion animal patients. The high safety and efficacy profiles of rifaximin suggest the potential for its use in veterinary patients. Initial pilot studies should confirm the presence of gastrointestinal excretion of unchanged drug in dogs and cats, the presence of elevated gastrointestinal concentrations of rifaximin, and the limited incidence of side effects. The drug could also have concurrent use in a variety of veterinary gastrointestinal diseases, including small intestinal bacterial overgrowth.

Use and safety of rifaximin in children with inflammatory bowel disease. Muniyappa P, Gulati R, Mohr F, Hupertz V. J PEDIATR GASTR NUTR 49:400-404, 2009.

Rifaximin treatment in hepatic encephalopathy. Bass NM, Mullen KD, Sanyal A, et al. N ENGL J MED 362:1071-1081, 2010.