PHARMACOKINETIC STUDY OF RIFAXIMIN AFTER ORAL-ADMINISTRATION IN HEALTHY-VOLUNTEERS

Eighteen healthy male volunteers, with a mean age of 24 yrs (range 18- 40), underwent an open pharmacokinetics study, aimed at defecting rifa ximin concentration in blood and urine after a single oral administrat ion of 400 mg of the antibiotic. Administration took place after a 9 h ours' fast and was followed by a breakfast after 2 hours and a lunch a fter 5 hours. Blood samples were collected before rifaximin administra tion and 1, 2, 4, 8, 12, 24 and 48 hours after dosing. Urine samples w ere collected immediately before dosing (reference sample) and then at the end of the following intervals of time: 0-6 h, 6-12 h, 12-24 h, 2 4-48 h. During the whole study period, the local and general tolerance to rifaximin administration was checked. Rifaximin concentration was assessed by reversed phase high performance liquid chromatography with electrochemical detection. In almost every plasma sample, rifaximin c oncentration was undetectable (lower than the detection limit of the a nalytical method, i.e. 2 ng/ml). In urine, very small amounts of the u nchanged molecule (<0.01% of the administered dose) were found in the period 0-48 hours. These results confirm the negligible absorption by the intestinal tract of a single oral dose of rifaximin (400 mg). Loca l and general tolerance of the administered drug was very good.