Levamisole has increasingly been discovered in street cocaine as an adulterant. Recent reports have linked levamisole in street cocaine to agranulocytosis in cocaine users. It is well known that agranulocytosis is associated with therapeutic use of levamisole, and this may have led to the withdrawal of the drug from the US market. Levamisole was a US Food and Drug Administration-approved drug that has been used as an immunomodulator, a chemotherapy adjuvant, and anthelmintic medication. The purpose of adulterating street cocaine with levamisole is not known, but it has been speculated that it is added intentionally in order to potentiate the effects of cocaine. This may be supported by the recent report of metabolism of levamisole to aminorex in racehorses. Aminorex and related compounds, specifically 4-methylaminorex, or "ice," have high abuse potential because of their amphetamine-like pharmacological activity. This metabolism has not been reported in humans, and therefore the intended role of levamisole in street cocaine remains an enigma.
Organophosphorus nerve agent (OPNA) adducts to butyrylcholinesterase (BChE) can be used to confirm exposure in humans. A highly accurate method to detect G-series and V-series OPNA adducts to BChE in 75 μL of filtered blood, serum, or plasma has been developed using immunomagnetic separation (IMS) coupled with liquid chromatography tandem mass spectrometry (LC-MS/MS). The reported IMS method captures > 88% of the BChE in a specimen and corrects for matrix effects on peptide calibrators. The optimized method has been used to quantify baseline BChE levels (unadducted and OPNA-adducted) in a matched set of serum, plasma and whole blood (later processed in-house for plasma content) from 192 unexposed individuals to determine the interchangeability of the tested matrices. The results of these measurements demonstrate the ability to accurately measure BChE regardless of the format of the blood specimen received. Criteria for accepting or denying specimens were established through a series of sample stability and processing experiments. The results of these efforts are an optimized and rugged method that is transferrable to other laboratories and an increased understanding of the BChE biomarker in matrix.
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