B-305 High Specificity Homogeneous Enzyme Immunoassay for Ketamine

A new immunoassay, the ARK Ketamine II Assay, accurately detects ketamine in human urine at two cutoff concentrations (50 and 100 ng/mL) with high precision and specificity. In tests on 223 negative urine samples, the assay correctly identified all as negative, including 22 that had produced a response above the detection limit in the earlier version. For positive samples confirmed by LC-MS/MS, the assay showed 100% sensitivity and 100% specificity at both cutoffs. The assay also cross-reacts with the major metabolite nor-ketamine at about 45–47%, while cross-reactivity to methoxetamine is less than 0.3%. The method is suitable for routine clinical chemistry analyzers.

Study at a glance

Abstract

Abstract Background Ketamine is a synthetic, nonbarbiturate and rapid-acting dissociative anesthetic that is indicated for use in both human and veterinary surgical procedures. Ketamine is a Schedule III substance under the United States Controlled Substances Act for its potential for abuse and risk of dependence. Ketamine is structurally and pharmacologically similar to phencyclidine (PCP), but is less potent, has a faster onset and shorter duration of action relative to PCP. Ketamine has abuse/dependence potential and is occasionally used as a recreational drug. Ketamine is prescribed off-label for various pain management and for treating depression. The ARK Ketamine II Assay has been developed to detect ketamine in human urine at cutoffs of 50 and 100 ng/mL with improved specificity. Methods The ARK Ketamine II Assay is a liquid-stable homogenous enzyme immunoassay consisting of two reagents. The assay has 50 ng/mL and 100 ng/mL cutoffs. The performance characteristics of this assay, including precision, spiked recovery, specificity, and method comparison to LC-MS/MS, were evaluated on the Beckman Coulter AU680 automated clinical analyzer. Results The ARK Ketamine II demonstrated acceptable precision, with no overlap at 50 ng/mL cutoff using ± 50% control levels (25 ng/mL and 75 ng/mL) and at 100 ng/mL cutoff using ± 25% control levels (75 ng/mL and 125 ng/mL) in a histogram overlap analysis, and less than 8.2% CV in semi-quantitative mode. Spiked ketamine samples spanning the semi-quantitative assay range of 500 ng/mL were recovered between 103.7% and 106.1% of the spiked levels from 20.0 to 500.0 ng/mL. The major metabolite, nor-ketamine at concentrations approximately equivalent to 50 ng/mL and 100 ng/mL cutoffs were determined at 110 ng/mL (45% cross-reactivity) and 210 ng/mL (47% cross-reactivity), respectively. The cross-reactivity to methoxetamine and its metabolites were determined to be <0.3%. In method comparison studies, the ARK Ketamine II Assay accurately identified all 223 human urine samples confirmed negative by LC-MS/MS as negative, including 22 samples which produce assay response above LoD in the original ARK Ketamine Assay. For positive patient samples confirmed by LC-MS/MS, ARK Ketamine II assay showed 100 % sensitivity and 100 % specificity for both cutoffs. Conclusion The ARK Ketamine II Assay is applicable to a wide range of clinical chemistry analyzers and provides a sensitive, rapid, and reliable measurement of ketamine in human urine.