Chlortetracycline in swine‐bioavailability and pharmacokinetics in fasted and fed pigs

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Abstract
Chlortetracycline hydrochloride was administered intra‐arterially (11 mg/kg) and as an oral drench (33 mg/kg) to ten 21.0‐31.5‐kg pigs. Five of the pigs were fasted 18 h prior to dosing and five of the pigs were fed ad libitum prior to dosing. The mean volume of distribution determined by area‐under‐the‐curve calculations for the fasted pigs (0.967 ± 0.210 1/kg) was significantly less (P < 0.05) than the mean volume of distribution for the fed pigs (1.39 ± 0.31 1/kg). Mean total body clearance of the drug was also significantly less (P < 0.05) in the fasted pigs (0.165 ± 0.055 1/kg/h) as compared to the fed pigs (0.307 ± 0.053 1/kg/h). The elimination constants (ß) were not found to be statistically different (P < 0.05): 0.1811 ± 0.0057 for the fasted pigs; 0.2260 ± 0.0461 for the fed pigs. The bioavailability for both groups was similar; 19.12 ± 8.3% for the fasted pigs and 17.88 ± 5.3% for the fed pigs.In a second experiment three groups of six pigs which weighed 34.5‐44.1 kg were fed a corn‐soy diet ad libitum. The rations were fortified with chlortetracycline at 100, 400 or 1000 mg chlortetracycline hydrochloride/kg feed. Chlortetracycline concentrations were determined in plasma samples collected over a 6‐day period. Plasma chlortetracycline concentrations reach a plateau within 24 h after initial access to the trial diets and were highly correlated with the dose of the drug consumed (r2= 0.97).