Homogeneous Enzyme Immunoassay for Cannabinoids in Urine

We describe a homogeneous enzyme immunoassay for measurement of cannabinoid metabolites, as well as 9-tetrahydrocannabinol (I) in urine. Malate dehydrogenase from pig heart mitochondria was labeled with a derivative of I. The compound used to calibrate the assay was the I metabolite, 1 1-nor-9-tetrahydrocannabinol-9-carboxylic acid (II). With 15 g of II per literof urine as the cutoff concentration, the assay can detect 25 tg of II per literwith>95 % confidence. A positive response was obtained for urine specimens assayed within 30 mm after exposure to cannabinoids. However, the persistence of metabolites of I in urine indicates that assay of this fluid is useful as an indicator of cannabinoid use but not as an indicator of in-toxication. Additional Keyphrases: marijuana drug abuse- toxi-cology. screening Several years ago a homogeneous enzyme immu-noassay was described (1) that made use of the obser-vation that certain enzymes, when covalently bound to haptens, could be inhibited by antibodies directed against the hapten. This technique, called EMIT,2 has been used clinically with three different enzymes, ly-sozyme (EC 3.2.1.17) (2), m-MDH3 (3, 4), and glucose-6-phosphate dehydrogenase (EC 1.1.1.49) (5, 6), to assay various compounds, including opiates, thyroxine, anti-epileptic drugs, and digoxin. Recently, using pig heart m-MDH conjugated with a derivative of 9-THC, we demonstrated that thi