July 13, 2011
When veterinarians think of regionally specific illness, toxicity caused by consumption of native plants and exposure to infectious organisms typically comes to mind.
In preparation for a move to Southern California, I studied the effects of sago palm ingestion and inhalation of Coccidioidomycosis with the anticipation of the conditions I would be diagnosing and treating in my clinical practice.
I did not anticipate that I would end up treating such a large number of dogs presenting with clinical signs consistent with marijuana (cannabis sativa) consumption. As the sale of medical marijuana is legal in many California cities, dispensaries provide human patients with smokable or edible products.
Unfortunately, humans can carelessly leave these products in locations accessible to their curious pets, leading to ingestion.
Although a pet could show signs of marijuana toxicity post-inhalation, the majority of cases I see are due to suspected or known oral ingestion. I have treated dogs almost exclusively, yet cats can be similarly affected. A 2002 study of 250 cases of marijuana exposure showed dogs to be the primary cannabis consumption culprits (96 percent). Cats followed in a distant second place (3 percent), and other species made up the smallest portion (1 percent).1
Mild cases present with lethargy, altered response to visual or verbal stimuli, injected (blood engorged) conjunctiva and behavior changes.
More severe cases display ataxia, hypothermia, hypotension, bradycardia, ptyalism, emesis, anorexia, urinary incontinence, diarrhea and dysphoria (vocalization). Coma and death are also possible in severe cases.
Clinical signs can occur within minutes to hours and can last for hours to days, in part due body fat storage of the active ingredients in marijuana.
A 2004 study of 213 dogs with oral marijuana exposure showed neurologic signs (lethargy, ataxia, dilated pupils, etc.) in 99 percent of patients. Gastrointestinal signs, such as vomiting, were seen in 30 percent of patients.2
Although marijuana can have an anti-nausea effect, the volume consumed in proportion to the patient’s body weight, other ingested ingredients, and the induced release of “feel-good” hormones like serotonin, can cause vomiting.
In a video available at VeterinaryPracticeNews.com/MarijuanaToxicity, an Italian greyhound that ingested marijuana overreacts to visual and audible cues, appears to have difficulty standing and walking, and ultimately ends up lowering itself to a sternal position on the ground in a staggered fashion.
Mechanism of Action
Marijuana contains delta-9-tetrahydrocannabinol (THC), which causes the release of the neurotransmitters acetylcholine, dopamine, norepinephrine and serotonin in the brain’s frontal cortex and cerebellum. The increased release of these neurotransmitters leads to the various clinical manifestations.
As the attending veterinarian, I consider the possibility of other factors contributing to the overall picture of health or illness. Did the pet consume only cannabis? Could prescription or over-the-counter human or veterinary medications, other recreational drugs or unknown intoxicating substances be involved?
Cannabis toxicity has a variety of differential diagnoses. Options include stimulants (ephedrine and ephedrine-like compounds, amphetamines, nicotine and methylxanthines found in chocolate), opioids, benzodiazepines, antidepressants, amitraz (such as that used in anti-parasitic collars), ivermectin (from heartworm preventives), bromethalin (rodenticides), ethylene glycol (antifreeze), and alcohol (ethanol from rotting fruit, bread dough, etc.).
The majority of cases I have treated presented with multiple clinical signs, leading to the top differential diagnosis of cannabis consumption. The diagnosis, however, may not necessarily be confirmed by the owner, who may be completely unaware that a pet was exposed to the drug.
Others are up front about their pets’ ingestion of cannabis. Most are somewhat reluctant to share the truth, but ultimately concede under gentle, direct questioning.
I always ask questions in a manner conveying my intention to help the pet and its treatment. In doing so, I create an environment where the owner can tell the truth, a realistic diagnosis can be achieved and I can expeditiously start the diagnostic and treatment process.
Besides the effects of THC, “edibles” can contain substances potentially adversely affecting a pet’s health. These include carbohydrates, fat, proteins, and other ingredients. Vomiting, diarrhea, anorexia, pancreatitis and other clinical signs can ensue and lead to further complications. The Italian greyhound in the video that ate the chocolate-, sugar- and butter-filled marijuana brownie created a rather unfavorable situation for itself after inquisitively snatching the goodie from the owner’s bag.
Having treated innumerable cannabis toxicities, I feel comfortable that my patients will make a full recovery with the appropriate care. If other toxins are suspected or known, I start a case file with the National Animal Poison Control Center (use weblink aspca.org/pet-care/poi
I perform baseline blood diagnostics to evaluate organ function. Knowing the status of the liver, kidneys and other body systems helps to rule out other underlying metabolic derangement that could contribute to the presenting clinical signs. I also recommend abdominal radiographs to look for gastrointestinal foreign bodies or other abnormalities.
For exposures occurring less than two hours before presentation, emesis is induced to clear the stomach of the intoxicant.
Once vomiting is under control, administration of activated charcoal can reduce absorption of certain toxins and speeds their evacuation through the gastrointestinal tract.
Provided a pet is not vomiting or comatose, administration of activated charcoal is a component to treating many cases of toxic exposure because of its ability to reduce enterohepatic recirculation of a toxic substance. Enterohepatic recirculation occurs after a toxin enters the bloodstream through the digestive tract, gets processed by the liver, then is excreted back into the small intestine via bile from the gall bladder.
Patients showing more profound sedation, ataxia, hypothermia, vomiting or other clinical signs are hospitalized for supportive care. Intravenous fluids, thermoregulatory support and anti-nausea and antacid medications promote a more rapid recovery and positive outcome.
Marijuana toxicity patients are typically discharged upon resolution of clinical signs and once they can hold down water and food.
Prevention is Best
The best way to avoid illness secondary to toxic exposure to any substance, including marijuana, is through prevention. Owners must pet-proof their homes with the same effort and attention to detail as they would baby proof for a human child.
Pets are intrigued by all sorts of smells, sounds and appearances, often curiously using their nasal and oral openings to evaluate anything within reach.
Clients can help prevent a pet’s toxic exposure by not bringing specific substances into the home or at least storing foods, medications and other household products where the animals can’t get them.
Dr. Mahaney is a Southern California veterinarian offering integrative veterinary medicine on a house call and in-facility basis through his business, California Pet Acupuncture and Wellness (CPAW) Inc., including acupuncture, Chinese herbs, nutritional and environmental modification and emergency medicine.
1. Janczyk P, Donaldson CW, Gualtney S: Two hundred and thirteen cases of marijuana toxicoses in dogs. Vet Hum Toxicol 2004 Vol 46 (1) pp. 19-21.
1. Shell, L: Marijuana Poisoning. Veterinary Information Network, 2006.
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