Comparison of four commercially available rapid test kits with liquid chromatography for detecting penicillin G residues in bovine plasma.

Four commercially available rapid tests (Brilliant Black reduction test, LacTek test, Charm Farm test, and Charm Test II receptor assay) were compared with a liquid chromatographic (LC) method (lowest quantitatable level of 5 ng/mL) in their efficiency, reliability, and sensitivity to detect penicillin G in bovine plasma. Samples were obtained from 16 steers treated with procaine penicillin G alone or in combination with its long-acting form, benzathine penicillin G. The steers were injected intramuscularly with penicillin G doses ranging from label dose to about 9 times label dose. When results of the Brilliant Black reduction, LacTek, Charm Test II, and Charm Farm tests for penicillin G in plasma (with detection sensitivities of 5, 10, 20, and 30 ng/mL, respectively) were compared with results of LC, none of the rapid tests gave false-positive results. Each rapid test elicited a positive response when used to test bovine plasma containing penicillin G residues at concentrations above the test's detection sensitivity. The simplicity, selectivity, and sensitivity of the rapid tests, coupled with rapidity with which results are obtained, make them suitable for use in large-volume preslaughter screening of penicillin-treated cattle.