Topical Review
Marijuana Poisoning

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Abstract

The plant Cannabis sativa has been used for centuries for the effects of its psychoactive resins. The term “marijuana” typically refers to tobacco-like preparations of the leaves and flowers. The plant contains more than 400 chemicals but the cannabinoid δ-9-tetrahydrocannabinol (THC) is the major psychoactive constituent. “Hashish” is the resin extracted from the tops of flowering plants and generally has a much higher THC concentration. Marijuana is the most commonly used illicit drug in the United States. Currently, several states have passed legislation to decriminalize possession of small amounts of marijuana for both medical and personal use and several other states have similar legislation under consideration. The most common form of marijuana use in humans is inhalation of the smoke of marijuana cigarettes, followed by ingestion. In animals, although secondhand smoke inhalation is possible, the most common source of exposure is through ingestion of the owner's marijuana supply. The minimum lethal oral dose for dogs for THC is more than 3 g/kg. Although the drug has a high margin of safety, deaths have been seen after ingestion of food products containing the more concentrated medical-grade THC butter. There are two specific cannabinoid receptors in humans and dogs, CB1 (primarily in central nervous system) and CB2 (peripheral tissues). In animals, following oral ingestion, clinical effects begin within 60 minutes. All of the neuropharmacologic mechanisms by which cannabinoids produce psychoactive effects have not been identified. However, CB1 activity is believed to be responsible for the majority of cannabinoid clinical effects. Highly lipid soluble, THC is distributed in fat, liver, brain, and renal tissue. Fifteen percent of THC is excreted into the urine and the rest is eliminated in the feces through biliary excretion. Clinical signs of canine intoxication include depression, hypersalivation, mydriasis, hypermetria, vomiting, urinary incontinence, tremors, hypothermia, and bradycardia. Higher dosages may additionally cause nystagmus, agitation, tachypnea, tachycardia, ataxia, hyperexcitability, and seizures. Treatment of marijuana ingestion in animals is largely supportive. Vital signs including temperature and heart rate and rhythm must be continually monitored. Stomach content and urine can be tested for cannabinoids. Gas chromatography and mass spectrometry can be utilized for THC detection but usually may take several days and are not practical for initiation of therapy. Human urine drug-screening tests can be unreliable for confirmation of marijuana toxicosis in dogs owing to the interference of a large number of the metabolites in canine urine. False negatives may also arise if testing occurs too recently following THC ingestion. Thus, the use of human urine drug-screening tests in dogs remains controversial. No specific antidote presently exists for THC poisoning. Sedation with benzodiazepines may be necessary if dogs are severely agitated. Intravenous fluids may be employed to counter prolonged vomiting and to help control body temperature. Recently, the use of intralipid therapy to bind the highly lipophilic THC has been utilized to help reduce clinical signs. The majority of dogs experiencing intoxication after marijuana ingestion recover completely without sequellae. Differential diagnoses of canine THC toxicosis include human pharmaceuticals with central nervous system stimulatory effects, drugs with central nervous system depressant effects, macrolide parasiticides, xylitol, and hallucinogenic mushrooms.

Introduction

For centuries, marijuana has been used both as a psychoactive intoxicant and for its hemp fiber used in rope.1 In the United States, mention of the use of marijuana as an intoxicant can be found in the popular literature starting in the 1850s. By the 1930s, the US Federal Bureau of Narcotics began to characterize marijuana as harmful and addictive. Marijuana was listed as a Schedule I drug (high potential for abuse without any recognized medical value or purpose) by the Controlled Substances Act in 1970.1

For the last 40 years, the decriminalization and legalization of certain types of marijuana use has been a highly controversial topic. In addition, marijuana has been reported to be effective in the treatment of a variety of medical conditions.2, 3 Despite a nationwide ban on its growth, sale, and utilization, US marijuana consumption has skyrocketed since the 1960s. At present, marijuana is the most commonly used illicit drug in the US.1, 4 In one study, 40% of Americans older than 12 years admitted that they had tried the drug at least once.1

During the last 3 decades, public opinion regarding prosecution for possession of small amounts of marijuana for personal use has changed dramatically. Although for most parts of the country, possession of any marijuana is illegal and federal law bans the drug, some states such as Arizona, California, Colorado, and Wisconsin have allowed the medicinal use of marijuana under certain circumstances with more states expected to follow suit. Nevertheless, Arizona, in 1997, passed legislation nullifying a physician's right to prescribe Schedule I substances (such as marijuana) without federal approval. In Colorado, in the general election of 2000, an amendment passed legalizing the sale and possession of marijuana for medical use. By 2010, there were 717 licensed medical marijuana dispensaries and 106,000 registered medical marijuana users in the state of Colorado.5, 6 In 2012, legislation passed in Colorado and Washington State decriminalizing the possession of small amounts of marijuana for personal use. Similar legislation in other states is expected. Dogs and cats are very susceptible to marijuana toxicosis but dogs are much more often affected. Marijuana poisoning in dogs results from inhalation of secondhand smoke; ingestion of the seeds, stems, leaves, and flowers; ingestion of products made from marijuana leaves (cookies, suckers, brownies, teas, etc.); and ingestion of products made with concentrated tetrahydrocannabinol (THC) or hashish oil. Because of the changes with regard to the legal status of marijuana making it more readily accessible, an increase in the number of accidental intoxications of pets (especially dogs) can be expected.

Section snippets

Sources

The plant Cannabis sativa is the source of marijuana. It has been used historically not only for its psychoactive resin but also for hemp fiber.1, 4 Cannabis was cultivated by the early North American colonists for use in making hemp ropes. “Marijuana” refers to any part of the plant, but generally, it has come to refer to the dried tobacco-like preparations of the leaves and flowers.1, 4, 7 Marijuana in its raw form comprises the dried and chopped stems, leaves, and seeds of the plant. C.

Toxic Dose

THC has a wide safety margin in dogs with the minimum lethal oral dose greater than 3 g/kg.13 This dose is 1000 times the dosage where behavioral effects are observed. Nevertheless, providing a true toxic dose for THC in mg/kg proves difficult because the degree of purity for marijuana varies so greatly and also depends upon the route of exposure. It should be pointed out that medical-grade THC butter used in baked goods may have a higher concentration of THC than of marijuana alone.6

Toxicokinetics and Mechanism of Toxicity

Almost all effects of a single exposure to marijuana (like most animals experience) can be predicted by the dose.4 THC is absorbed readily when smoked. Oral ingestion produces similar pharmacologic effects, but the absorption after ingestion is slower and more erratic than by smoking.1, 4, 6, 9 The onset of psychoactive effects following cannabis ingestion is unpredictable when compared with smoking. Oral absorption of THC can be increased with the ingestion of fatty foods.9 In dogs, following

Clinical Signs

The various effects of THC exposure, including time of onset, duration of effect, and severity of clinical signs, depend upon the dose and the route of administration of the drug. In dogs, clinical signs include ataxia and incoordination, hypersalivation, depression, disorientation, hypothermia, mydriasis, bradycardia, vomiting, and tremors.6, 9, 10, 14 In one study, nearly half of the dogs displayed urinary incontinence.6 The authors postulated that dogs exposed to medical-grade marijuana may

Minimum Database

Although THC intoxication is not reflected in either a complete blood count or a biochemical blood panel, blood should be drawn in marijuana suspects to rule out other causes for the clinical signs or the presence of concurrent medical conditions. Body temperature and heart rate and rhythm must be continually monitored during the course of therapy.9, 14

Confirmatory Tests and Diagnostics

Taking a medical history is an essential skill. For a variety of reasons, owners may give histories that are inaccurate, unreliable, and sometimes purposely deceitful. Owners may deliberately falsify a history owing to fear of legal repercussions and potential grounds for prosecution.21 Nowhere is there a greater potential for an untruthful history as in the case of an animal's ingestion of an illicit drug. Veterinary clinicians must gain the confidence of the client quickly so as to obtain a

Treatment

There is no specific antidote for cannabis.1, 4, 9, 14 Emesis may be unrewarding; THC has been shown to have a significant antiemetic effect.22 Emesis can be initiated if the ingestion was recent (within the last 2 hours) but should never be employed if signs of CNS stimulation are present, if the animal is severely agitated, or if the animal is severely depressed or unresponsive. Treatment objectives in cases of marijuana toxicosis are prevention of further absorption and supportive care.

Prognosis and Prevention

Although recovery in dogs following marijuana toxicosis may be prolonged (up to 5 days), the majority of dogs ingesting THC recover completely with no long-term adverse effects.9, 14 Severity of the poisoning is dose dependent, and animals exposed to higher dosages require longer and more aggressive therapy.6 Dogs that ingest medical-grade THC butter and food products containing the butter have been shown to be more at risk for serious intoxication and require more involved and prolonged

Histologic Lesions

For the majority of animals, intoxication with marijuana is an acute, 1-time event. As a result, no long-term histologic lesions have been described in animals poisoned by THC. In humans, where repetitive and chronic marijuana use is common, heavy marijuana smokers show a high prevalence of pulmonary immune cells. In addition, heavy marijuana smokers had a much higher incidence of bronchitis and precancerous cells in the bronchial epithelium.4 In rats, high doses of THC administered during

Differential Diagnoses

A correct diagnosis of marijuana intoxication may be initially missed owing to a purposely misleading history by the owners, the nonspecific clinical signs characteristic of THC toxicosis, and the current paucity of reliable laboratory tests confirming this poisoning. Furthermore, the avenue of exposure in these cases is not always immediately evident. Potential look-alikes for marijuana toxicosis are numerous and differentials must include opioids, lysergic acid diethylamide, phencyclidine

References (28)

  • P.A. Volmer

    “Recreational” drugs

  • G.R. Thompson et al.

    Comparison of acute oral toxicity in rats, dogs, and monkeys

    Toxicol Appl Pharmacol

    (1973)
  • K.T. Fitzgerald

    Taking a toxicological history

  • M. McGuigon

    Cannabinoids

  • S.M. Bagshaw et al.

    Medical efficacy of cannabinoids and marijuana: a comprehensive review of the literature

    J Palliat Care

    (2002)
  • B. Martin et al.

    Marijuana

  • Warner J: Medical marijuana dispensary applications: 700 plus, earning Colorado 7 Million. Westword,...
  • S.D. Meola et al.

    Evaluation of trends in marijuana toxicosis in dogs living in a state with legalized medical marijuana: 125 dogs (2005-2010)

    J Vet Emer Crit Care

    (2012)
  • C.W. Donalson

    Marijuana exposure in animals

    Vet Med

    (2002)
  • E.A. Voth et al.

    Medicinal applications of delta-9 tetrahydrocannabinol and marijuana

    Ann Intern Med

    (1997)
  • P. Janczyk et al.

    Two hundred thirteen cases of marijuana toxicosis in dogs

    Vet Human Toxicol

    (2004)
  • Synthetic Drug Control Act of 2011, A.R. 1254....
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