Chiral sensitivity of medetomidine lateral flow immunoassay test strips

Medetomidine has recently emerged in the illicit drug supply in the United States, and lateral flow immunoassay test strips are an inexpensive and easy-to-use field screening option for detecting this highly potent sedative. However, the drug is chiral, and the response of test strips to the different enantiomers has not been reported. This study evaluated the chiral sensitivity of 7 lots of medetomidine test strips produced by two manufacturers. Test strips were assessed using solutions of dexmedetomidine, levomedetomidine, and racemic medetomidine at varying concentrations, water types, and temperature conditions. Specificity was evaluated by testing structurally related compounds and other interferences. Multiple lots of medetomidine strips responded only to dexmedetomidine. These strips detect racemic medetomidine but give a negative result for pure levomedetomidine. Other lots of medetomidine strips required both dexmedetomidine and levomedetomidine to be present to give a positive result-either pure dexmedetomidine or pure levomedetomidine gave negative results. All strips performed best in 18 MΩ water. at temperatures of 25 °C or below. Xylazine did not cross-react. The veterinary sedative detomidine HCl caused false positives on all the strips at concentrations down to 0.07 mg/mL, and levamisole gave faint test lines (which can be misread as false positives) for almost all the strips at 2 mg/mL. Organizations selecting test strips for public health applications should select strips that can detect both dexmedetomidine and racemic versions of this sedative.