title: Pharmacokinetics, bioavailability, and in vitro antibacterial activity of rifampin in the horse.
abstract: The pharmacokinetics and bioavailability of rifampin were determined after IV (10 mg/kg of body weight) and intragastric (20 mg/kg of body weight) administration to 6 healthy, adult horses. After IV administration, the disposition kinetics of rifampin were best described by a 2-compartment open model. A rapid distribution phase was followed by a slower elimination phase, with a half-life (t1/2[beta]) of 7.27 +/- 1.11 hours. The mean body clearance was 1.49 +/- 0.41 ml/min.kg, and the mean volume of distribution was 932 +/- 292 ml/kg, indicating that rifampin was widely distributed in the body. After intragastric administration of rifampin in aqueous suspension, a brief lag period (0.31 +/- 0.09 hour) was followed by rapid, but incomplete, absorption (t1/2[a] = 0.51 +/- 0.32 hour) and slow elimination (t1/2[d] = 11.50 +/- 1.55 hours). The mean bioavailability (fractional absorption) of the administered dose during the first 24 hours was 53.94 +/- 18.90%, and we estimated that 70.0 +/- 23.6% of the drug would eventually be absorbed. The mean peak plasma rifampin concentration was 13.25 +/- 2.70 micrograms/ml at 2.5 +/- 1.6 hours after dosing. All 6 horses had plasma rifampin concentrations greater than 2 micrograms/ml by 45 minutes after dosing; concentrations greater than 3 micrograms/ml persisted for at least 24 hours. Mean plasma rifampin concentrations at 12 and 24 hours after dosing were 6.86 +/- 1.69 micrograms/ml and 3.83 +/- 0.87 micrograms/ml, respectively. We tested 162 isolates of 16 bacterial species cultured from clinically ill horses for susceptibility to rifampin.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Medicine, School of Veterinary Medicine, University of California, Davis 95616.
authors.forename: W D
authors.initials: WD
authors.lastname: Wilson
authors.forename: M S
authors.initials: MS
authors.lastname: Spensley
authors.forename: J D
authors.initials: JD
authors.lastname: Baggot
authors.forename: S K
authors.initials: SK
authors.lastname: Hietala
mesh_terms: D000818:Animals; D001424:Bacterial Infections / Q000188:drug therapy / Q000662:veterinary; D001682:Biological Availability; D005260:Female; D006734:Horse Diseases / Q000188:drug therapy; D006736:Horses / Q000378:metabolism* / Q000382:microbiology; D008826:Microbial Sensitivity Tests; D012293:Rifampin / Q000493:pharmacokinetics* / Q000494:pharmacology
chemical_list: D012293:Rifampin