Ampicillin and amoxicillin residue detection in milk, using microbial receptor assay (Charm II) and liquid chromatography methods, after extra-label administration of the drugs to lactating cows

Kevin L. Anderson From the Departments of Food Animal and Equine Medicine (Anderson) and Anatomy, Physiological Sciences, and Radiology (Papich), College of Veterinary Medicine, and Departments of Food Science (Rushing) and Animal Science (Wesen), College of Agricultural and Life Sciences North Carolina State University, Raleigh, NO 27606, and USDA, Meat Science Research Laboratory, Beltsville, MD 20705 (Moats)

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William A. Moats From the Departments of Food Animal and Equine Medicine (Anderson) and Anatomy, Physiological Sciences, and Radiology (Papich), College of Veterinary Medicine, and Departments of Food Science (Rushing) and Animal Science (Wesen), College of Agricultural and Life Sciences North Carolina State University, Raleigh, NO 27606, and USDA, Meat Science Research Laboratory, Beltsville, MD 20705 (Moats)

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John E. Rushing From the Departments of Food Animal and Equine Medicine (Anderson) and Anatomy, Physiological Sciences, and Radiology (Papich), College of Veterinary Medicine, and Departments of Food Science (Rushing) and Animal Science (Wesen), College of Agricultural and Life Sciences North Carolina State University, Raleigh, NO 27606, and USDA, Meat Science Research Laboratory, Beltsville, MD 20705 (Moats)

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Donald P. Wesen From the Departments of Food Animal and Equine Medicine (Anderson) and Anatomy, Physiological Sciences, and Radiology (Papich), College of Veterinary Medicine, and Departments of Food Science (Rushing) and Animal Science (Wesen), College of Agricultural and Life Sciences North Carolina State University, Raleigh, NO 27606, and USDA, Meat Science Research Laboratory, Beltsville, MD 20705 (Moats)

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Mark G. Papich From the Departments of Food Animal and Equine Medicine (Anderson) and Anatomy, Physiological Sciences, and Radiology (Papich), College of Veterinary Medicine, and Departments of Food Science (Rushing) and Animal Science (Wesen), College of Agricultural and Life Sciences North Carolina State University, Raleigh, NO 27606, and USDA, Meat Science Research Laboratory, Beltsville, MD 20705 (Moats)

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Abstract

Objective

A microbial receptor assay method (MRAM; Charm II test) for β-lactam antibiotics and a liquid chromatography (LC) method with a detection limit of 2 to 5 ppb were evaluated for detection of ampicillin or amoxicillin residues in milk samples from individuell cows.

Design

The MRAM was compared to the LC in 2 respects. Measured concentrations of drugs were compared, as well as the classification of samples relative to the FDA tolerance value of 10 ppb.

Animals

A total of 6 clinically normal lactating Holstein cows were used per drug.

Procedure

Ampicillin trihydrate or amoxicillin trihydrate was administered at an extra-label dosage of 22 mg/kg of body weight, IM, once to each of 6 cows/drug. Milk samples were collected at milkings prior to and for 156 hours after drug administration. Drug concentrations in milk samples from individual cows were determined by use of the MRAM and LC tests. Additionally, the classification of milk samples relative to the presence or absence of residues above the FDA tolerance value was determined. Pharmacokinetic analysis was performed on derived milk drug concentrations.

Results

Concentration of ampicillin in milk samples from all cows was < 10 ppb by the MRAM and LC methods by the fourth milking (48 hours) after treatment with ampicillin. Values were < 10 ppb by both methods for all cows treated with amoxicillin by the sixth milking (72 hours) after treatment. For individual milk samples, significant differences were found between test methods in the proportion of positive (failing) tests; the MRAM had a higher proportion of presumptive positives.

Conclusions

Even at an extra-label dosage of 22 mg/kg, IM, milk residues > 10 ppb (the FDA tolerance value) were not detected beyond the label milk withholding times for ampicillin (48 hours) and amoxicillin (96 hours). When used for testing milk of individual cows by the control point procedure, the MRAM had a tendency to give presumptive positive test results for milk samples containing < 10 ppb ampicillin or amoxicillin as determined by LC. (Am J Vet Res 1996;57:73-78)

Abstract

Objective

A microbial receptor assay method (MRAM; Charm II test) for β-lactam antibiotics and a liquid chromatography (LC) method with a detection limit of 2 to 5 ppb were evaluated for detection of ampicillin or amoxicillin residues in milk samples from individuell cows.

Design

The MRAM was compared to the LC in 2 respects. Measured concentrations of drugs were compared, as well as the classification of samples relative to the FDA tolerance value of 10 ppb.

Animals

A total of 6 clinically normal lactating Holstein cows were used per drug.

Procedure

Ampicillin trihydrate or amoxicillin trihydrate was administered at an extra-label dosage of 22 mg/kg of body weight, IM, once to each of 6 cows/drug. Milk samples were collected at milkings prior to and for 156 hours after drug administration. Drug concentrations in milk samples from individual cows were determined by use of the MRAM and LC tests. Additionally, the classification of milk samples relative to the presence or absence of residues above the FDA tolerance value was determined. Pharmacokinetic analysis was performed on derived milk drug concentrations.

Results

Concentration of ampicillin in milk samples from all cows was < 10 ppb by the MRAM and LC methods by the fourth milking (48 hours) after treatment with ampicillin. Values were < 10 ppb by both methods for all cows treated with amoxicillin by the sixth milking (72 hours) after treatment. For individual milk samples, significant differences were found between test methods in the proportion of positive (failing) tests; the MRAM had a higher proportion of presumptive positives.

Conclusions

Even at an extra-label dosage of 22 mg/kg, IM, milk residues > 10 ppb (the FDA tolerance value) were not detected beyond the label milk withholding times for ampicillin (48 hours) and amoxicillin (96 hours). When used for testing milk of individual cows by the control point procedure, the MRAM had a tendency to give presumptive positive test results for milk samples containing < 10 ppb ampicillin or amoxicillin as determined by LC. (Am J Vet Res 1996;57:73-78)

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