Veterinary : Poisoning/Toxicosis
Apomorphine to Stimulate Vomiting
Emetic drugs are usually administered
in emergency situations after ingestion of a toxin. “Apomorphine
is an opiate drug that acts as a potent central dopamine agonist
to directly stimulate the CTZ. It can be administered PO, IV, or
SC; the IM route is not as effective. It can also be applied directly
to conjunctival and gingival membranes, using the tablet formulation,
which can easily be removed once emesis is initiated. Vomiting
usually occurs in 5-10 min. Although apomorphine directly stimulates
the CTZ, it has a depressant effect on the emetic center. Therefore,
if the first dose does not induce emesis, additional doses are
not helpful. Because the vestibular apparatus may also be involved
in apomorphine-induced vomiting, animals that are sedate and motionless
will not vomit as readily as animals that are active. Because it
can cause CNS stimulation, apomorphine is used cautiously in cats.
Opiate-induced excitement in cats can be treated with naloxone
(an opiate antagonist).”
Apomorphine dosage for dogs: 4 mg/kg PO; 0.02 mg/kg IV; 0.3 mg/kg
SC (from Merck Veterinary Manual, 8th edition, p. 1681); 0.25mg/kg
(as a tablet) into the conjunctival sac (from Plumb’s Veterinary
Drug Handbook, p.51)
“is not a rare event; and veterinarians need to have access to antidotes.
However, there are relatively few products specifically labeled for use in these
instances, so it has not really been legal for veterinarians to have previously
prepared antidotes for poisonings on hand in emergency rooms. For example, if
a case of lead poisoning is diagnosed and the veterinarian needs some calcium
EDTA as an antidote, there is no product available labeled for use in animals...
Compounding offers opportunities for facilities to have [items such as calcium
EDTA] on hand ... for emergency treatment, in anticipation of a legitimate prescription.”
Intl J of Pharm Comp 1997 July/Aug; 1(4): 240
N-acetylcysteine as an Antidote for Acetaminophen Toxicosis
N-acetylcysteine (NAC) is the antidote of choice for the treatment of acetaminophen
poisoning, one of the most common types of intoxication in dogs and cats.
NAC acts principally by replenishment of intracellular glutathione stores
and detoxification of the reactive metabolite (NAPQI). NAC acts as a scavenger
of free radicals, blocks the conversion of hemoglobin to methemoglobin,
and can reduce the extent of liver injury.
Although NAC is most effective if administered less than 12 hours after ingestion
of acetaminophen, the use of NAC as an antidote is still recommended up
to 36 to 80 hours after acetaminophen ingestion.
Oral NAC, IV NAC, and IV sodium sulfate were evaluated as treatments for
cats who had received toxic sublethal doses of acetaminophen (APAP).
At the dosage levels used, oral NAC, IV NAC, and IV sodium sulfate were
equally effective antidotes, as measured by decreased methemoglobinemia,
increased whole blood reduced glutathione, decreased APAP half-lives, and
increased urinary excretion of the APAP-sulfate conjugate. All the antidotal
treatments produced results significantly different from those in the control
To determine if rectally administered N-acetylcysteine (NAC) is absorbed
into the systemic circulation, NAC was administered into the rectal
vault (2.0 g/kg) of swine via a balloon-tipped Foley catheter inserted into
the animals' rectums. NAC administered via the rectal route resulted
in systemic absorption as determined by spectrophotometric methods
in 5 of the 7 study animals. This study provides important information regarding
the development of a potential alternative route for the administration
of NAC to dogs.
In dogs and cats, NAC can be administered intravenously or orally,
but has a pungent odor. Oral administration of NAC typically causes
nausea and vomiting. The oral solution can be compounded as a chicken-flavored
preparation to improve palatability.
Rapid intravenous administration of NAC can cause hypotension, bronchospasm,
and flushing. Reactions can be minimized by slowing the rate of
Activated charcoal may absorb NAC and reduce its effectiveness,
so NAC should not be administered within two hours of giving activated
of activated charcoal may exacerbate vomiting and lead to aspiration.
A strong antiemetic agent (metoclopramide 0.4 mg/kg IV) may be
necessary to prevent emesis.”
NAC is currently not approved by the FDA for use in dogs and cats,
but is available in human formulations, and upon a prescription
order, can be compounded to meet specific veterinary needs.
Compendium 2003 Apr;25(4):276-280
Am J Vet Res 1985 Jul;46(7):1485-9
here to access the PubMed abstract of this article.
Vet Hum Toxicol 1997 Dec;39(6):329-31
Vet Med 1997;92(2):158-165
Dimercaptosuccinic Acid for Lead Poisoning in Cats
Wright Veterinary Medical Center, Bethlehem, PA
The owners of two nine-year-old cats moved to a new house. One week after
moving, both cats were vomiting and losing weight so the owners brought the
cats to the veterinary clinic. The veterinarian began intravenous hydration.
Blood work showed a very high level of nucleated RBC's. The CBC revealed platelet
clumps on feathered edge, few macrocytes, moderate anisocytosis, and occasional
acanthocytes (54% and 45.1% NRBC). One cat had two seizures on the first
day of hospitalization. Based on the initial signs and nucleated red cells,
lead poisoning was suspected, although there was no radiographic evidence of
lead ingestion. We tested for lead and began treatment with dimercaptosuccinic
acid (DMSA) 40mg/cc.
The cats improved clinically within 24 hours. There were no more seizures
and the cats began to eat. The blood lead levels were 164.8 and 210 (normal
is 0-25). The cats were treated with 40mg (1cc) of DMSA given orally three
times per day for a total of 10 days. DMSA is not commercially available
in an injectable or liquid form. Therefore, we worked together with our
compounding pharmacist to prepare a sterile formulation that would be suitable
for intravenous or oral use.
The second day after therapy had begun, the owners
informed us that they had been sanding the painted floors in their new house.
The cats probably walked through the dust and in grooming themselves licked
the lead paint off their paws. There have been no further problems with the
cats to our knowledge. The owner declined to come in for a lead level recheck.
Penicillamine for Long-Term Treatment of Lead Poisoning
Penicillamine chelates a variety of metals, including copper, lead, iron
and mercury, forming stable water-soluble complexes that are excreted by the
kidneys. Used primarily for its chelating ability in veterinary medicine,
it is the drug of choice for copper storage-associated hepatopathies in
dogs at a dose of 15mg/kg PO twice daily. Penicillamine may also be used in
cystine urolithiasis (penicillamine combines chemically with cystine to form
a stable soluble complex that can be readily excreted) and in a different dose
for the long-term oral treatment of lead poisoning. “This drug should preferably
be given on an empty stomach, at least 30 minutes before feeding. If the
animal develops problems with vomiting or anorexia, three remedies have been
suggested. 1) Give the same total daily dose, but divide into smaller individual
doses and give more frequently. 2) Temporarily reduce the daily dose and
gradually increase to recommended dosage. 3) Give with meals (will probably
reduce amount of drug absorbed).”
Veterinary Drug Handbook, 2nd edition, Donald C. Plumb, Ed.
4-Methylpyrazole for Ethylene Glycol (Antifreeze) Poisoning
Therapy for ethylene glycol poisoning is aimed at preventing absorption,
increasing excretion, and preventing metabolism of ethylene glycol to its toxic
metabolites. Inhibition of liver alcohol dehydrogenase (ADH), the enzyme responsible
for the initial reaction in the metabolic pathway, can be accomplished by giving
a compound that combines with the enzyme and renders it inactive. The most
effective ADH inhibitor in the dog is 4-methylpyrazole (4-MP), which unlike
most competitive inhibitors (ethanol, propylene glycol, and 1,3-butanediol)
does not contribute to CNS depression and increased serum osmolality. The
recommended dose of 5% (50mg/ml) 4-methylpyrazole is 20 mg/kg body weight
IV initially, followed by 15 mg/kg IV at 12 and 24 hr, and 5 mg/kg at 36
hr. While 4-MP is the recommended therapy in dogs, it is not appropriate
for use in cats. Although it is non-toxic, it does not effectively inhibit
EG metabolism unless administered to a cat at the same time as consumption
Am J Vet Res 1995;56:825.