Jj. Descombe et al., PHARMACOKINETIC STUDY OF RIFAXIMIN AFTER ORAL-ADMINISTRATION IN HEALTHY-VOLUNTEERS, International journal of clinical pharmacology research, 14(2), 1994, pp. 51-56
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.