Pemoline and tetramisole 'positives' in english racehorses following levamisole administration

Gabapentin, a human therapeutic medication and an environmental substance transferring at trace levels to horses: a case report

Gabapentin, 1-(Aminomethyl)cyclohexaneacetic acid, MW 171.240, is a frequently prescribed high dose human medication that is also used recreationally. Gabapentin is orally absorbed; the dose can be 3,000 mg/day and it is excreted essentially unchanged in urine. Gabapentin is stable in the environment and routinely detected in urban wastewater. Gabapentin randomly transfers from humans to racing horses and is at times detected at pharmacologically ineffective / trace level concentrations in equine plasma and urine. In Ohio racing between January 2019 and July 2020,18 Gabapentin identifications, all less than 2 ng/ml in plasma, were reported. These identifications were ongoing because the horsemen involved were unable to pin down and therefore avoid the source of these identifications. Given that 44 ng/ml or less is an Irrelevant Plasma Concentration (IPC) of Gabapentin in horses, we proposed a 5 ng/ml plasma interim Screening Limit of Detection for Gabapentin identifications in Ohio racing, and an essentially similar 8 ng/ml plasma Screening Limit of Detection was suggested by a scientific advisor to the Ohio Horse Racing Commission. As such, an analytical Screening Limit of 8 ng /ml in plasma is an appropriate and pharmacologically conservative analytical "cut-off" or Screening Limit of Detection (SLOD) for Gabapentin in equine competitive events to avoid the calling of "positive" identifications on random unavoidable trace level identifications of this widely prescribed human therapeutic medication in equine forensic samples.

The medication violations in racehorses at Louisiana racetracks from 2016 to 2020

Introduction/Background

The number of publications for most common drug violations in racehorses is limited. This study reports the most common medication violations in racehorses at four major racetracks in Louisiana between 2016 and 2020.

Methods

During this 5‐year period, 27,237 blood samples and 25,672 urine samples collected during the course of normal race meeting activities were analysed by initial screening procedure utilizing Liquid Chromatography Mass Spectrometry (LC‐MS/MS). Following initial screening, suspect samples were subject to quantitative or semi‐ quantitative confirmation analysis by LC‐MS/MS.

Results

The total number of violations reported was 534 (1.01% of the total number of specimens analysed). The total number of violations reported in Thoroughbred horses was 210 while the total number of violations reported in Quarter Horses was 324. The percentage of total violations was %0.59 for all the specimens analysed in Thoroughbred horses while this percentage was %1.9 for all the specimens analysed in Quarter Horses during this 5‐year period. The most frequent violations included the overages (concentrations of permitted medications equal to or exceeding the set threshold) of clenbuterol (165 violations), non‐steroidal anti‐inflammatory drugs (NSAIDs) such as phenylbutazone (73 violations), combination of phenylbutazone with flunixin (45 violations) and muscle relaxant methocarbamol (40 violations).

Discussion/Conclusions

The total number of violations were relatively low during 5‐year period, but wide varieties of medications with different pharmacological actions were confirmed in performance horses in Louisiana. The most frequently reported violations in Louisiana were for permitted therapeutic medications (clenbuterol, phenylbutazone, flunixin methocarbamol) with established threshold and/or withdrawal guidelines in racehorses.

Levamisole-a Toxic Adulterant in Illicit Drug Preparations: a Review

ABSTRACT

Discovered in the 1960s, the common anthelminthic levamisole has seen widespread use in veterinary applications. Its use rapidly expanded thereafter to include human medical treatments for a variety of acute and chronic disorders. Because of reports of severe adverse effects, the US Food and Drug Administration withdrew levamisole's approval for human use in 2000; however, medical options outside the United States and illicit options worldwide allow continued accessibility to levamisole. The compound is rapidly metabolized in the body, with at least 2 known active metabolites. Levamisole has a broad range of immunomodulatory effects, including both stimulatory and inhibitory effects on immune responses. It is generally well tolerated at therapeutic concentrations, although a variety of autoimmune-related adverse effects have been reported, including agranulocytosis, leukopenia, purpura, and visible necrotized skin tissue. Individuals with levamisole-compromised immune systems are more susceptible to infections, including COVID-19. Since the early 2000's, levamisole has been frequently used as an adulterating agent in illicit street drugs, especially cocaine, fentanyl, and heroin. Although its prevalence has varied over time and geographically, levamisole has been detected in up to 79% of the street supply of cocaine at levels up to 74% by weight. Its presence in illicit drug markets also raises concern over the potential for exposure of children and neonates, although this is supported by only limited anecdotal evidence. Levamisole is not currently included in routine drug testing panels, although a variety of confirmatory testing techniques exist across a range of antemortem and postmortem specimen options. Because of its varying presence in illicit drug markets, both the medical and forensic communities need to be aware of levamisole and its potential impact on toxicological investigations.

Synthesis and characterization of barbarin, a possible source of unexplained aminorex identifications in forensic science

Aminorex is a US DEA Schedule 1 controlled substance occasionally detected in racing horses. A number of aminorex identifications in sport horses were thought to have been caused by exposure to plant sources of aminorex. Glucobarbarin, found in plants of the Brassicaceae family, has been suggested as a potential proximate chemical source by being metabolized in the plant or the horse to aminorex. In Brassicaceae, glucobarbarin is hydrolyzed by myrosinase to yield barbarin, which serves as an insect repellant and/or attractant and is structurally related to aminorex. The synthesis, purification, and characterization of barbarin is now reported for use as a reference standard in aminorex related research concerning equine urinary identifications of aminorex and also for possible use in equine administration experiments. Synthesis of barbarin was performed via ring closure between phenylethanolamine and carbon disulfide in tetrahydrofuran with the catalyst pyridine under reflux. The reaction yielded a white crystalline substance that was purified and chemically characterized as barbarin for use as a Certified Reference Standard or for studies related to equine aminorex identification.

Aminorex identified in horse urine following consumption of Barbarea vulgaris; a preliminary report

Background

Aminorex, (RS)-5- Phenyl-4,5-dihydro-1,3-oxazol-2-amine, is an amphetamine-like anorectic and in the United States a Drug Enforcement Administration [DEA] Schedule 1 controlled substance. Aminorex in horse urine is usually present as a metabolite of Levamisole, an equine anthelmintic and immune stimulant. Recently, Aminorex identifications have been reported in horse urine with no history or evidence of Levamisole administration. Analysis of the urine samples suggested a botanical source, directing attention to the Brassicaceae plant family, with their contained GlucoBarbarin and Barbarin as possible sources of Aminorex. Since horsepersons face up to a 1 year suspension and a $10,000.00 fine for an Aminorex identification, the existence of natural sources of Aminorex precursors in equine feedstuffs is of importance to both individual horsepersons and the industry worldwide.

Results

Testing the hypothesis that Brassicaceae plants could give rise to Aminorex identifications in equine urine we botanically identified and harvested flowering Kentucky Barbarea vulgaris, (“Yellow Rocket”) in May 2018 in Kentucky and administered the plant orally to two horses. Analysis of post-administration urine samples yielded Aminorex, showing that consumption of Kentucky Barbarea vulgaris can give rise to Aminorex identifications in equine urine.

Conclusions

Aminorex has been identified in post administration urine samples from horses fed freshly harvested flowering Kentucky Barbarea vulgaris, colloquially “Yellow Rocket”. These identifications are consistent with occasional low concentration identifications of Aminorex in equine samples submitted for drug testing. The source of these Aminorex identifications is believed to be the chemically related Barbarin, found as its precursor GlucoBarbarin in Kentucky Barbarea vulgaris and related Brassicaceae plants worldwide.

Plasma and Urine Levamisole in Clinical Samples Containing Benzoylecgonine: Absence of Aminorex

Aminorex has been reported as a metabolite of levamisole in man, but data on the aminorex concentrations in clinical samples are scant. We thus measured levamisole, aminorex and benzoylecgonine in urine, and levamisole and aminorex in plasma using achiral liquid chromatography-high resolution mass spectrometry. Centrifuged urine (50 μL) was diluted with LC eluent containing internal standard (benzoylecgonine-D3, 25 μg/L) (450 μL). For plasma, sample (200 μL) and Tris solution (2 mol/L, pH 10.6, 100 μL) were added to a 60.5 × 7.5 mm i.d. glass test tube. Internal standard solution (ketamine-D4, 200 μg/L) (10 μL) was added and the tube contents vortex-mixed (5 s). Butyl acetate:butanol (9 + 1, v/v; 200 μL) was added and after vortex-mixing (30 s) and centrifugation (13,680 × g, 4 min), the extract was evaporated to dryness and reconstituted in 10 mmol/L aqueous ammonium formate containing 0.1% (v/v) formic acid (150 μL). Prepared samples and extracts (100 μL) were analyzed using an AccucoreTM Phenyl-Hexyl column (2.6 mm a.p.s., 100 × 2.1 mm i.d.) maintained at 40°C. MS detection was in positive mode using heated electrospray ionization (ThermoFisher Q-ExactiveTM). Intra- and inter-assay accuracy and precision were ±20%, and ≤11%, respectively, for all analytes in both matrices. Lower limits of quantitation were 0.1 and 1 μg/L (all analytes) in plasma and urine, respectively. Of 100 consecutive urine samples submitted for drugs of abuse screening containing benzoylecgonine, levamisole was detected in 72 (median 565, range 4-72,970 μg/L). Levamisole was also measured in eight plasma samples (median 10.6, range 0.9-64.1 μg/L). A number of metabolites of levamisole (4-hydroxylevamisole, levamisole sulfoxide, levamisole glucuronide, and hydroxylevamisole glucuronide) were tentatively identified in urine. Neither aminorex, nor any of its reported metabolites were detected in any sample.

Neurologic Conditions Affecting the Equine Athlete

EPM, CVSM, and EDM are currently recognized as the 3 most common neurologic diseases in US horses, with the latter 2 conditions being most prevalent in young animals. Moreover, horses competing at shows and performance events are at greater risk for exposure to highly contagious, neurologic EHV-1 outbreaks. A clinical diagnosis of any neurologic disease should be based on a careful history, complete neurologic examination, and appropriate diagnostic testing and interpretation. However, mild or early neurologic signs can often mimic or be mistaken for an orthopedic condition when horses present for performance-related concerns.

Using chemical bond-based method to predict site of metabolism for five biotransformations mediated by CYP 3A4, 2D6, and 2C9

Although it has been proposed for decades to predict site of metabolism (SOM) by in silico methods, identifying SOM correctly remains an unsolved fundamental problem and is an active area of research. In our prior works, we proposed a chemical bond-based approach to construction of SOM prediction models by integrating chemical bond descriptors and drug-metabolizing enzymes data. Although it has been evaluated with both 10-fold cross-validation and independent validation, we believe comparisons between this method and prior methods using publicly accessible external datasets are indispensable and more desirable. In the current study, based on chemical bond-based method, metabolism data released by Sheridan et al. and Zaretzki et al. was utilized to establish metabolite prediction models for CYP450 3A4, 2D6, and 2C9. Five major reaction types were involved, including Aliphatic C-hydroxylation, Aromatic C-hydroxylation, N-dealkylation, O-dealkylation, and S-Oxidation. Consequently, all our five models showed impressive performance on predicting SOMs, with accuracy and area under curve exceeded 0.940 and 0.953, respectively. Compared to prior works, our models were better than SOMP both in "SOM-scale" and "molecule-scale". In conclusion, comparisons between chemical-bond based method and prior works were conducted for the first time, which demonstrated that chemical-bond based method is better than or at least comparable to prior works.

Therapeutics for Equine Protozoal Myeloencephalitis

Equine protozoal myeloencephalitis is an infectious disease of the central nervous system caused by Sarcocystis neurona or Neospora hughesi. Affected horses routinely present with progressive and asymmetrical neurologic deficits. The diagnosis relies on the presence of neurologic signs, ruling out other neurologic disorders, and the detection of intrathecally derived antibodies to either S neurona and/or N hughesi. Recommended treatment is use of an FDA-approved anticoccidial drug formulation. Medical and supportive treatment is provided based on the severity of neurologic deficits and complications. This article focuses on recent data related to diagnosis, pharmacologic treatment, and prevention.

A clinician's guide to factors affecting withdrawal times for equine therapeutic medications

Equine forensic science can now detect concentrations down to 25 femtograms/mL (parts per quadrillion, ppq) or less in blood and urine. As such, horsemen are increasingly at risk of inadvertent 'positives' due to therapeutic medication 'overages' or trace identifications of dietary or environmental substances. Reviewed here are the factors which determine detection times and 'withdrawal times' for substances administered to horses. Withdrawal times are affected by many factors, including dose, formulation, route and frequency of administration, bioavailability, plasma half-life, sensitivity of the analytical process, the testing matrix (plasma, urine, or other), and the environmental presence and/or persistence of administered substances. Of these factors only dose is known precisely. For any given administration, horse-to-horse differences in the volumes of distribution, systemic clearance, and terminal plasma elimination half-life of substances are major and totally uncontrollable factors driving horse-to-horse variability in withdrawal times. A further complication is that chemically stable medications administered to horses and eliminated in the urine inevitably become part of the environment of the horse. The presence of these substances in the equine environment is increasingly giving rise to trace identifications long after nominal administration of these substances has ceased. Because of the unknown and uncontrollable horse-to-horse variability in medication pharmacokinetics, any therapeutic medication administration to a horse by definition includes the possibility of an inadvertent medication overage. As such, the caveat that there are no guarantees in life most assuredly applies to advisories concerning equine therapeutic medication withdrawal times.

Levamisole in cocaine: unexpected news from an old acquaintance

Levamisole is a pharmaceutical with anthelminthic and immunomodulatory properties that was previously used in both animals and humans to treat inflammatory conditions and cancer. Levamisole has been identified as a cocaine adulterant in the United States since 2003. By 2009, the United States Drug Enforcement Administration (DEA) estimated that 69% of the cocaine seized contained levamisole. The first case reports of complications related to levamisole in cocaine users were published in 2009. The objectives of this article are to review the literature regarding the full spectrum of possible complications related to levamisole use for medical purposes, to review the current scope of levamisole-induced complications in cocaine users and to discuss the pharmacological properties that might explain the motivation behind the large-scale adulteration of cocaine with levamisole. Literature review revealed that significant complications were quickly reported when levamisole was used in inflammatory conditions. By 1976, several cases of leukopenia and agranulocytosis were reported. Recurrence with re-exposure was well described and agranulocytosis spontaneously reversed upon discontinuation of therapy. Vasculitis secondary to levamisole treatment was first reported in 1978 and mostly manifests as leukocytoclastic vasculitis, cutaneous necrotising vasculitis and thrombotic vasculopathy without vasculitis. These findings typically, but not invariably, involve the ear lobes. Discontinuation of levamisole therapy was again a critical part of the treatment. Various neurological side effects were described with levamisole therapy, the most concerning complication being multifocal inflammatory leukoencephalopathy (MIL). Literature review identified 203 unique cases of complications in cocaine users that can be attributed to levamisole adulteration. The two principal complications reported are haematological (140 cases of neutropenia) and dermatological (84 cases). Even though these complications can occur in isolation, many cases displayed both simultaneously. No formal case of leukoencephalopathy in the setting of cocaine use has been reported so far. A striking phenomenon is the apparent high level of recurrence (27.1%) of symptoms in cocaine users after re-exposure to cocaine that is presumably adulterated. The importance of accurately identifying levamisole-induced complications is therefore critical for symptomatic patients as discontinuation of exposure is fundamental and as a correct diagnosis prevents unnecessary and potentially dangerous use of other treatment modalities like powerful immunosuppressive therapy. Literature review suggests that levamisole might have the advantages of enhancing noradrenergic neurotransmission by inhibiting reuptake, by inhibiting MAO and/or COMT, by acting on ganglionic nicotinic receptors and by being partially metabolized into an amphetamine-like compound. It could also increase endogenous opioids and increase dopamine concentration in the cerebral reward pathway. These potential effects make levamisole an interesting choice as a cocaine adulterant. It seems unlikely that levamisole use as a cocaine adulterant will soon reach an end. More information is needed about the diagnosis and treatment of levamisole-induced complications, and the efforts of the medical and public health community is needed to face this challenging problem.