Acute, subacute, chronic toxicity and mutagenicity studies of rifaximin (L/105) in rats.

Acute, subacute and chronic toxicity-mutagenicity studies of rifaximin (L/105), a new semisynthetic rifamycin SV antibiotic, were conducted in rats. The oral LD50 value for this species was greater than 2000 mg/kg. Rifaximin given orally to rats up to 6 months produced no evident adverse effects up to 100 mg/kg. The moderate effects noted were probably due to the topical action of the drug. Rifaximin did not show any mutagenic activity when compared with mutagenic standards.