New level of drug testing for milk residue screening

Researchers have adopted a new drug testing techniques in the screening of milk residue pharmaceuticals, saying that conventional tests are not suited to testing milk.

More sensitive screening tests are being deployed by regulatory authorities to test pharmaceuticals used for the treatment of disease in lactating cows causing violative milk residues that may pose a risk to human health.

The Cyclone Custom Analyte Detection Service (CYCADS) group at Iowa State University’s College of Veterinary Medicine are using liquid chromatography–mass spectrometry (LC-MS) screening test that gives a similar level of assay to the one used by the Food and Drug Administration and other regulatory authorities.

Hans Coetzee, from the centre, said there are several issues with current testing methods. He said: "Qualitative immunoassays used for routine drug screening are cost effective and provide rapid results, but these are generally non-specific tests for ‘inhibitory substances’ and not specific compounds. They often only detect the presence of these substances at certain levels in the milk as opposed to determining the actual concentrations that may be present."

He added: "Producers would benefit from having access to a highly sensitive and specific confirmatory test similar to the one used by regulatory authorities to determine actual drug concentrations in milk."

The test is available at a much lower cost than what is usually associated with conducting this type of screening in other labs. The main use for the test is to identify and quantify drug concentrations in samples that tested positive in conventional screening, but came from cattle with no treatment history. It could also be used for cattle that are outside the recommended milk withdrawal period for a product that was administered previously.

Other uses include drug depletion in milk after a drug has been administered in an extra-label manner, and analysis of milk recently purchased cattle prior to them joining the rest of the herd as part of a herd biosecurity protocol.

Posted by Fiona Griffiths