Page 421 - Veterinary Toxicology, Basic and Clinical Principles, 3rd Edition

388 SECTION | IV Drugs of Use and Abuse

VetBooks.ir approximately 1% THC; whereas a more recent average These baked goods are attractive to dogs and possibly
other companion animals and are a common source of
THC concentration in seized marijuana samples was recent
exposure.
average THC concentration in seized marijuana samples
was 10.1% (Anonymous, 2011). Hashish can contain more New synthetic cannabinoids, which aren’t structurally
than 10% THC; hashish oil can contain more than 20% related to THC but can have exponentially higher
THC and may be added to a marijuana cigarette to double potency, have been developed since the 1960s, but have
the potency. only become popular in the United States since around
There are a variety of accepted and controversial med- 2008. There are currently hundreds of these compounds
ical uses for marijuana and its active compound. Though available on the market (Rech et al., 2015). One is 1-
still illegal under federal law, some states allow posses- penthyl-3-(1-naphthoyl) indole, or JWH-018, which is
sion and use of marijuana, often under certain conditions mixed with leafy herbs and sold as “spice” or “K2” to be
and for medical treatment. Though laws change fre- smoked as an alternative to marijuana. These products are
quently, as of this writing more than half of the states in readily available, frequently as “incense” and typically
the US allow some form of marijuana use. Prescription marked “not for human consumption,” but are inten-
products include dronabinol (Marinol) capsules, which tionally smoked, ingested, or taken parenterally. Laws
contain THC in sesame oil and remain classified as a concerning these products vary by country, state, and city
Schedule I drug by the DEA, and Nabilone (Cesamet), a and are made more complicated by the difficulty in iden-
synthetic form of THC classified as Schedule II. These tifying and testing for new compounds entering the mar-
drugs are used to treat nausea in cancer patients and may ket. Adverse effects in dogs that have been exposed to
be superior in efficacy to other antiemetic drugs. They synthetic cannabinoids have been reported.
improve weight gain among patients with AIDS, cancer, Large animals have been exposed through grazing
or Alzheimer’s disease and have been considered for use marijuana or ingesting dry baled marijuana as hay
in the treatment of glaucoma, multiple sclerosis, chronic (Cardassis, 1951; Driemeier, 1997). Horses have been
pain, epilepsy and various psychiatric disorders (Di bedded on hemp fiber, which presents an impaction risk
Marzo and De Petrocellis, 2006). (Green, 1996; Smith and Papworth, 1996).
Illegal marijuana is most commonly used in the form
of marijuana cigarettes called “joints” or “reefers.” Toxicity
Alternately, marijuana may be rolled in a tobacco leaf
Few veterinary deaths have been reported from marijuana
and called a “blunt” or smoked using a water pipe
intoxications. Marijuana has a very wide safety margin in
(“bong”) or other type of pipe. Marijuana may be brewed
that the lethal dose is approximately 1000 times the effec-
into a tea, or more commonly baked into brownies, cook-
tive dose (Volmer, 2005). No deaths were reported in dogs
ies, or cakes (Ashton, 2001; Volmer, 2005). Many veteri-
and monkeys ingesting 3 9 g of marijuana per kg of body
nary exposures come from the ingestion of tainted baked
weight (Burrows and Tyrl, 2001). Janczyk et al. (2004)
goods.
documented the survival of a dog that ingested 26.8 g mari-
Marijuana cigarettes are sometimes dipped in a mix-
juana/kg body weight. The LD 50 for oral marijuana expo-
ture of phencyclidine, methanol, and formaldehyde.
sure in rats is 666 1000 mg/kg (Kisseberth and Trammel,
Ketamine, opium, cocaine, and heroin may be added to a
1990; Burrows and Tyrl, 2001). Driemeier (1997) reports
marijuana cigarette or used with marijuana. Street names
that four out of five debilitated cattle died after the group
for marijuana include “grass,” “hemp,” “Mary Jane” or
ingested 35 kg of dried marijuana. Horses and mules have
“MJ,” “pot,” “puff,” and “weed.”
died after ingesting large quantities of fresh marijuana of
Dogs less than 1 year of age are the most likely com-
the species Cannabis indica (Cardassis, 1951).
panion animal to ingest marijuana (Kisseberth and
Trammel, 1990; Janczyk et al., 2004). Marijuana leaves
or marijuana cigarettes were recovered from 203 of 213 Toxicokinetics
canine ingestions. Fresh plants and refined resins are also Absorption of inhaled THC approaches 50% and clinical
occasionally available to companion animals. Intentional signs occur in 6 12 min (Burrows and Tyrl, 2001;
intoxication of small animals using second-hand smoke Janczyk et al., 2004). Gastrointestinal absorption is erratic
has been reported (Schwartz and Riddle, 1985; Buchta, in humans and dogs. Blood concentrations obtained by
1988; Frohne and Pfa ¨nder, 2004). THC is highly fat- ingestion are 25% 30% of those obtained by smoking in
soluble. Marijuana can be processed with a source of fat, humans (Ashton, 2001). Onset of clinical signs is usually
such as butter, allowing the THC to partition into the lipid delayed at least 30 min after ingestion.
matrix, which can be used in cooking. This “pot butter” is Circulating THC is up to 99% protein bound in
now frequently used to make baked goods containing humans (Volmer, 2005). Plasma concentrations peak
high concentrations of THC (Fitzgerald et al., 2013). within 2 3 h. This lipid soluble compound is rapidly