Tissue distribution and elimination kinetics of oxytetracycline in sixteen organs and body fluids were determined in young pigs following intravenous and oral administration. Seventeen non‐fasted pigs, 8–10 weeks of age, weight range 16.4–34.5 kg were dosed intravenously at a dose rate of 11 mg/kg bodyweight. An additional seventeen weaning pigs, 12–14 weeks of age, weight range 27.2–36.3 kg were dosed orally at a dose rate of 48–65 mg/kg bodyweight. Oxytetracycline was rapidly distributed (half‐life, 6.71 ± 1.13 min) in swine. The mean volume of distribution was 1.26 ± 0.18 l/kg and overall body clearance was 3.82 ± 0.59 ml/kg/min. The elimination half‐life of oxytetracycline in pigs was 3.87 ± 0.62 h, which is shorter than has been observed in other domestic animal species. Oxytetracycline became rapidly and efficiently involved in enterohepatic cycling, with as much as 70% of a total intravenous dose being available for reabsorption from the gastrointestinal tract within 1 h after administration. This high degree of enterohepatic recycling prolonged the half‐life, and the large amount of drug that entered the enteric tract contributed to the high volumes of distribution and high k12/k21 ratios. The excellent tissue penetration of this drug further contributed to the high volume of distribution and high k12/k21 ratios obtained. Relationships between plasma and tissue depletion for several major edible organs were found to be statistically significant. Blood plasma is proposed as a body fluid for monitoring oxytetracycline tissue residues.

Eighteen non‐fasted, 12–16 week old pigs weighing between 20 and 40 kg were dosed with chloramphenicol intravenously at a dose rate of 22 mg/kg body weight. The pharmacokinetics of chloramphenicol were determined in blood plasma and sixteen selected organs and body fluids. The elimination half‐life in plasma was estimated to be 2.66pL1.06 h and volume of distribution was 1.39pL0.32 I/kg. The body clearance of chloramphenicol was estimated to be 6.64pL1.52 ml/kg/min. The elimination half‐life in tissue was found to range from 1.25 h in kidney to 5.89 h in fat. Most major organs ranged from 2.0 to 5.0 h. Significant correlations were found to exist between plasma concentrations and most major organ concentrations. Chloramphenicol concentrations in muscle, spleen, lung, stomach content, and large intestine content were found to exist slightly beyond the time when concentrations were negative in plasma. However, urine levels exceeded tissue levels at the last slaughter interval. It appears that serum or urine would be a good body fluid for monitoring chloramphenicol residues in tissues, whereas stomach content might be used as an indicator for chloramphenicol treatment for many days after therapy with the drug.

A 40-year-old Asian man, 6 months post renal transplant and receiving tacrolimus therapy, presented to the emergency department with a complaint of sudden-onset left eye pain with blurred vision, headache on the left side, and nausea and vomiting. On being admitted, the patient was intubated for respiratory depression, and erythromycin was initiated for suspected atypical pneumonia. Tacrolimus concentrations (whole blood) drawn on the 3rd day of hospitalization were reported to be > 60.0 ng/ml. Before hospitalization, tacrolimus concentrations were reported to be 9.8 ng/ml on a maintenance dose of 7 mg twice daily. Six days after discontinuation of erythromycin and a decrease in tacrolimus dose, the concentration decreased to 11.5 ng/ml and the original dose of tacrolimus was restarted. It is recommended that concurrent administration of erythromycin and tacrolimus be avoided. However, if concomitant therapy is necessary, tacrolimus concentrations, serum creatinine, blood urea nitrogen, and urine output should be monitored.

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Twenty‐two young cross‐bred swine were treated either intravenously or orally with potassium penicillin G. The pharmacokinetics of penicillin G were determined in plasma and tissues. The plasma half‐life of penicillin G in swine was found to be 19.45±1.69 min, and the distribution and elimination kinetics were found to fit a classical two‐compartment model. The volume of distribution was found to be 0.53±0.12 1/kg, and the body clearance was found to be 19.06±5.06 ml/min/kg which exceeded the effective renal plasma flow of 16.50±2.73 ml/min/kg, suggesting that the drug was eliminated both by tubular excretion and glomerular filtration. The elimination rate constants (Beta) for the major organs were as follows: muscle, 0.00343 min‐1; lung, 0.0310 min‐1; fat, 0.0394 min‐1; and kidney, 0.0213 min‐1, which compared favorably with the elimination rate constant found in plasma (0.0320 min‐1). These values were found to be significantly similar at the level of P < 0.005 in muscle, spleen and fat, and at a level of P < 0.025 in lung tissue. The data indicates that blood plasma would be a satisfactory body fluid for estimating this drug in tissue.