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Abstract

Objective—To determine tissue depletion of penicillin G in calves after oral ingestion with milk replacer and estimate a withdrawal period.

Design—Longitudinal controlled trial.

Animals—26 Holstein calves.

Procedure—Once daily, 24 calves were fed milk replacer containing procaine penicillin G (0.68 mg/kg [0.31 mg/lb] of body weight); 2 calves served as controls. After 1 feeding, 12 calves were euthanatized in groups of 3 each 4, 6.5, 9.5, and 13 hours after feeding. After 14 days, 12 calves were euthanatized in groups of 3 each 4, 6.5, 9.5, and 13 hours after the final feeding. Concentrations of penicillin G were determined in tissues, blood, and urine by use of high-performance liquid chromatography.

Results—Penicillin G was not detected in muscle samples of treated calves. The highest concentrations of penicillin G in plasma, kidney, and liver were 13 ng/ml, 92 ng/g, and 142 ng/g, respectively. Thirteen carcasses had violative drug residues; 12 had violative residues in the liver only, and 1 had violative residues in the liver and kidney. A 21-hour withdrawal period was estimated.

Conclusions and Clinical Relevance—Liver had the highest concentration of penicillin G and was most likely to have violative residues. Feeding calves milk containing penicillin G has the potential to cause violative drug residues in tissues. It is recommended to observe an appropriate withdrawal time prior to slaughter if calves are fed milk from cows treated with penicillin G. (J Am Vet Med Assoc 2001;219: 346–350)

Full access
in Journal of the American Veterinary Medical Association

Summary

Plasma concentration of penicillin G was evaluated in beef steers after administration of either a combination of benzathine penicillin G and procaine penicillin G in a 1:1 mixture at a dosage of 9,000 U/kg of body weight, im (n = 5), 24,000 U/kg, im (n = 5), or 8,800 U/kg, sc (n = 5), or benzathine penicillin G alone at a dosage of 12,000 U/kg, im (n = 7). Plasma concentration of penicillin G was measured by use of a high-performance liquid chromatography assay that had a limit of determination of 0.005 µg/ml. At a dosage for this combination of 9,000 U/kg im, and 8,800 U/kg, sc, which are approved label recommendations in Canada, and the United States, respectively, mean (± sem) peak plasma concentration was 0.58 (± 0.15) and 0.44 (± 0.02) µg/ml, respectively. Although plasma penicillin concentration was quantifiable for 7 days in the steers that received 9,000 U/kg, im, and for 4 days in the steers that received 8,800 U/kg, sc, the concentration was < 0.1 µg/ml in both groups after the first 12 hours. After administration of the combination at dosage of 24,000 U/kg, im, there was an initial peak plasma concentration at approximately 2 hours; thereafter, plasma concentration decreased slowly, with half-life of 58 hours. Although plasma penicillin G concentration was quantifiable for 12 days at this dosage, concentration was < 0.1 µg/ml after the first 48 hours. After the initial 48 hours, plasma concentration of penicillin was of similar magnitude and decreased at similar rate for the combination at dosage of 24,000 U/kg and for 12,000 U/kg of benzathine penicillin G alone. Most of the plasma penicillin G concentration in the first 24 hours after administration of a 1:1 combination of benzathine penicillin G and procaine penicillin G is attributable to absorption of procaine penicillin G. After the first 48 hours, most of the plasma drug concentration appeared to be produced by absorption of penicillin G from benzathine penicillin G. Absorption of benzathine penicillin G produces quantifiable plasma penicillin G concentrations for several days, but they are below the level of susceptibility for most bacteria.

Free access
in American Journal of Veterinary Research