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of its use as a recreational drug and its powder formulation, residues of cocaine are occasionally found in blood and urine samples collected from horses in drug and medication control programs.

       Prohibited substance under USEF, FEI, AQHA, and ARCI regulations.

ETIOLOGY/PATHOPHYSIOLOGY

      Mechanism of Action

       The pharmacodynamics of cocaine involve the complex relationships of multiple neurotransmitters.

       It directly prevents the re‐uptake of dopamine, serotonin, and norepinephrine into presynaptic neurons.

       Like other local anesthetics, it produces direct effects on cell membranes – cocaine blocks sodium channel activity and thus prevents the generation and conduction of nerve impulses in electrically active cells, such as myocardial and nerve cells.

      Toxicokinetics

       Cocaine has not been well studied in the horse. Based on the scientific literature examining the effects of cocaine in other species, however, in the horse one would expect it to be well absorbed when administered via mucous membranes (e.g. intranasally) or the GI tract.

       In humans, peak concentrations occur within 5–10 minutes of smoking and within 60 minutes of intranasal administration.

       Some cocaine is excreted unchanged in the urine, but the vast majority is metabolized to benzoylecgonine, ecgonine methyl ester, norcocaine and other metabolites.

       Although cocaine has a short elimination half‐life, the half‐lives of cocaine metabolites are substantially longer.

      Toxicity

       The lethal dose for cocaine in horses has not been determined and there are no reports of acute toxicity in the scientific literature.

       In mice the LD50 is reported to be 96 mg/kg following oral administration.

       In humans, recreational cocaine abusers typically have peak serum concentrations between 0.5 and 5 μM, but lethal toxicity has been observed with serum concentrations of cocaine of 10 μM.

      Systems Affected

       Neurological – ataxia, disorientation, euphoria, agitation, anxiety, seizures.

       Cardiovascular – tachydysrhythmia, severe hypertension, acute coronary syndrome in humans, stroke.

       Musculoskeletal – hyperthermia, cocaine‐induced rhabdomyolysis.

SIGNALMENT/HISTORY

      Risk Factors

       Accidental ingestion is unlikely.

       Illicit administration for performance‐enhancing effects in racehorses could occur.

       Inadvertent exposure from by a human abuser or from a contaminated environment is theoretically possible.

      Historical Findings

       Owners and trainers may be reluctant to admit possession and use.

       In many cases, the source may not be identified.

      Location and Circumstances of Poisoning

       Worldwide problem, not just limited to the United States.

       Intentional exposure by direct administration to horse.

       Unintentional exposure by careless placement of product or inadvertent transfer from personnel could theoretically cause detectable concentrations of cocaine or its metabolites to be present in blood and urine samples, but toxic concentrations are unlikely.

CLINICAL FEATURES

       With pharmacologically significant doses:CNS stimulation.Tachycardia.Arrhythmias.Bilateral mydriasis.Increased locomotor activity.

       Many exposures are not pharmacologically significant, although they produce detectable concentrations of cocaine metabolites in urine and blood samples.

DIFFERENTIAL DIAGNOSIS

       CNS stimulants (amphetamines, methamphetamine).

       High doses of beta2‐adrenergic agonists.

       High doses of caffeine or other methylxanthines.

DIAGNOSTICS

      CBC/Serum Chemistry/Urinalysis

       BUN, creatinine, and creatine kinase for evidence of rhabdomyolysis

      Serum Samples/Urine Samples

       Immunoassay screening.

       LC‐MS.

      Other Diagnostic Tests

       ECG as needed for tachydysrhythmia and cardiac effects.

      Pathological Findings

       None reported in the horses, but from other species, if dose was high enough one would predict:Myocardial necrosis and hemorrhage.Pulmonary hemorrhage.

THERAPEUTICS

      Appropriate Health Care

       Monitor ECG and treat arrhythmias.

       Maintain blood volume, pH, and electrolyte balance.

       Monitor for hyperthermia.

       Avoid CNS stimulation; dark quiet stall if possible.

      Antidotes

      No specific antidote.

      Drugs of Choice

       IV fluids as needed.

       For excitation:Detomdine 20–40 μg/kg IV.Romifidine 40–120 μg/kg IV.

       Control life‐threatening cardiac arrhythmias:Propranolol 0.02 mg/kg IV slowly, maximum of 1 mg/kg.Esmolol CRI 25–75 μg/kg/min.

      Precautions/Interactions

       Ethanol potentiates the effects and may increase the risk of toxicity.

       Protection