Page 423 - Veterinary Toxicology, Basic and Clinical Principles, 3rd Edition

390 SECTION | IV Drugs of Use and Abuse

VetBooks.ir may be due to the increased use of medical-grade mari- Pathology
juana products and baked goods that use “pot butter” and
There is little information on lesions associated with mari-
contain other compounds such as methylxanthines.
Treatment for THC exposure includes decontamina- juana overdose in small animals because so few have
died. Pulmonary edema was noted in a cow (Driemeier,
tion with supportive and symptomatic care. Mild intoxica-
1997). C. indica was identified in the stomach of the
tion only requires observation most of the time.
horses with edema as well as petechiation of the gastric
Gastrointestinal decontamination to decrease THC absorp-
wall and myocardial hemorrhage (Cardassis, 1951).
tion can be used in animals that have ingested large quan-
tities of marijuana or more concentrated marijuana
products. Emesis can be attempted with great caution in Barbiturates
animals believed to have ingested a high dose of THC
Barbiturates are derived from the nonsedative barbituric
within the past hour if they remain asymptomatic but
acid. They are a bitter tasting white powder in the pure
must be avoided in animals with clinical signs such as
form and are most frequently available as a sodium salt in
CNS depression or remarkable agitation (Dumonceaux
a weakly acidic aqueous solution. Barbiturates have been
and Beasley, 1990; Dumonceaux, 1995). Repeated dosing
used in anesthesia, sedation, and seizure control, and
with activated charcoal and cathartics can prevent absorp-
though still commonly used by veterinarians, are becoming
tion and enterohepatic cycling and thus decreases the
more uncommon in human medicine (Kisseberth and
duration of clinical signs, but this too must be used judi-
Trammel, 1990). The four classifications of barbiturates
ciously (Fitzgerald et al., 2013). Keeping the patient in an
are based on the duration of their activities. The expected
area with minimal external stimulation (low light, activ-
duration of an ultrashort-acting barbiturate in general is
ity, and noise) and appropriate symptomatic care will be
approximately 20 min with a duration of approximately
adequate treatment most of the time. Recovery can take
3 h. These drugs are given IV to effect for anesthesia.
several days. THC is highly lipid soluble, and, in the
Examples include thiamylal sodium and thiopental sodium,
author’s experience, intravenous (IV) lipid infusion can
both Schedule III, and methohexital sodium, which is
be used to diminish clinical signs of the THC toxicosis in
Schedule IV. The duration of short-acting barbiturates,
dogs (unpublished information).
which are given IV for anesthesia, is approximately 3 h.
Observation of the patient includes monitoring cardiac
Common examples of these are pentobarbital sodium and
function, body temperature and respiration. Stuporous or
secobarbital sodium, both Schedule II drugs. The duration
comatose dogs are at risk for respiratory suppression or
of intermediate-acting barbiturates, such as butobarbital or
hypothermia and must be treated appropriately. Marked
amobarbital, both Schedule III, is 3 6 h. Long-acting
central nervous stimulation can be treated with diazepam.
barbiturates can produce clinical effects for 12 h and these
Treatment of large animals was not attempted in the
drugs have use in sedation and anticonvulsant therapy.
few cases presented in the literature. The rapid onset and
Phenobarbital, methylphenobarbital, and barbital sodium
progression of clinical signs in the horses did not allow
are examples of long-acting barbiturates and are Schedule
time for veterinary intervention. Basic treatment procedures
IV drugs (Kisseberth and Trammel, 1990; Branson, 2001;
in large animals parallel those used in small animals.
Volmer, 2005). Barbiturates are known as downers, reds,
Gastrointestinal decontamination for large ingestions can
Christmas trees, and dolls on the illegal market.
involve gastric lavage or, in cattle, rumenotomy, and intra-
Barbiturate overdose in companion animals is usually
gastric or intraruminal instillation of mineral oil or acti-
iatrogenic or due to accidental ingestion of prescription or
vated charcoal and cathartics. Monitoring and symptomatic
illicit drugs. A common problem in veterinary medicine is
and supportive care should proceed as above.
exposure to carcasses of animals that were euthanized
Two dog deaths were recently reported in dogs that
with barbiturates. This problem has been diagnosed by
ingested baked goods made with marijuana butter (Meola
the author and reported in dogs and in wildlife in the liter-
et al., 2012). One dog presented minimally responsive
ature (Humphreys et al., 1980; Branson, 2001; Volmer,
and was treated with IV lipid infusion but died with coa-
2005). According to the AVMA News, in 2003, at least
gulopathy on the second day of treatment. The second
34 bald eagles have died from pentobarbital poisoning.
presented unresponsive and underwent aggressive decon-
Veterinarians and animal owners are responsible for
tamination measures but developed respiratory difficulty
proper carcass disposal and may be liable for wildlife
and died, possibly because of aspiration pneumonia.
poisonings (Volmer, 2005).
Veterinary laboratories test blood or plasma for THC
using gas chromatography/mass spectrometry (GC/MS) or
immunoassays. Drug testing kits are available over the Toxicity
counter from pharmacies but are unlikely to be useful The LD 50 for pentobarbital in dogs is 40 60 mg/kg by
in dogs. the IV route or 85 mg/kg per os. The oral LD 50 for cats is