1. The pharmacokinetics and bioavailability of enrofloxacin in chickens were investigated following intravenous, intramuscular, subcutaneous and oral administration of 10 mg/kg body weight. A rapid distribution phase was followed by a slower elimination phase. 2. The apparent volume of distribution was 2.2 l/kg. Absorption half lives were 0.37, 0.36 and 0.92 h; elimination half lives were 4.06, 4.48 and 4.29 h and bioavailabilities were 87.5%, 80.8% and 59.6% after intramuscular, subcutaneous and oral administration, respectively. The drug completely disappeared from all tissues after 3 days following oral administration. 3. Based on the bioavailability and disposition kinetics of enrofloxacin, administration of one dose per day should both be practical and adequate to maintain plasma enrofloxacin concentrations within the pharmacologically active but lower than tolerance limit.

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1. Chickens were given either a single dose of chloramphenicol (50 mg/kg body weight per os) or a dose of chloramphenicol together with pyridoxine (25 mg/kg per os) given 1 h before or 4 h afterwards. 2. Concentrations of chloramphenicol were determined in samples of serum and the rates of distribution and elimination extrapolated. Concentrations of chloramphenicol in muscle, liver and kidney were also determined. 3. Serum concentrations of chloramphenicol were lower in chickens given both pyridoxine and chloramphenicol compared with those given only chloramphenicol. 4. Differences were most pronounced during the post-absorptive phase. The rates of disappearance of chloramphenicol residues from tissues were enhanced by pyridoxine. 5. The biological half life of chloramphenicol and area under the concentration-time curve were both reduced by the concurrent administration of pyridoxine. 6. Availability of pyridoxine may be a rate limiting factor in the biotransformation of xenobiotics, though its indiscriminate use could cause failure of antibiotic therapy.