Trace-level detections of methamphetamine in racing horses – a review and forensic analysis

Methamphetamine is a central stimulant and an approved human therapeutic medication which is also clandestinely synthesized and marketed worldwide as a recreational substance. Users of clandestinely synthesized methamphetamine may handle and use methamphetamine in far greater amounts than medically approved dosages. Given that mucous membrane exposure of a horse to 10 milligrams of methamphetamine has produced jugular blood plasma/serum methamphetamine concentrations of 88,400 picogram/ml, inadvertent transfer of picogram/ml amounts of methamphetamine from recreational users to racing horses is a well understood process. Evaluating such picogram/ml methamphetamine identifications, the first factor to consider is that methamphetamine presents as two chemically distinct mirror image enantiomers, d-methamphetamine and l-methamphetamine. d-Methamphetamine is the more pharmacologically active enantiomer, marketed in the United States (US) as Desoxyn^®, a US Drug Enforcement Administration (DEA) Schedule II prescription medication. l-Methamphetamine is pharmacologically less active and is marketed in the US in several Over-The-Counter (OTC) nasal decongestant inhalers. Forensically correct evaluation of picogram/ml jugular blood/plasma/serum methamphetamine identifications in racing horses requires quantitative evaluation of the blood, urinary and hair concentrations of each methamphetamine enantiomer, as well as the presence or absence of the expected amphetamine metabolite. Evaluation of the regulatory significance of a jugular blood/plasma/serum concentration of methamphetamine must also take into account the fact that following oral exposure to methamphetamine jugular blood concentrations will be much higher than systemic blood concentrations, given that the jugular vein is the direct venous connection between the local high mucous membrane concentration of methamphetamine and the systemic circulation of the horse. Based on published scientific data, mucous membrane exposure of a horse to 100 micrograms of methamphetamine, a very conservative 1/1,500 of a possibly pharmacologically effective equine dose may give rise to jugular blood/plasma/serum concentrations of methamphetamine of 884 picograms/ml, a conservative guideline value for evaluating the pharmacological and forensic significance of jugular blood/plasma/serum concentrations of methamphetamine.