LONG ACTING ANTICOAGULANT RODENTICIDES
A report was recently forwarded to us by Dr. Charles McCune
of Indianapolis
of a dog taken to a practitioner after known ingestion of
an anticoagulantrodenticide. The dog was treated, as is accepted
practice, by the practitioner with injectable vitamin K and
released. Ten days later the dog developed massive hemorrhages
and was taken to Dr. McCune. In spite of supportive treatment
and additional vitamin K therapy, the dog died. The purpose
of this report is to emphasize the fact
that single treatment of toxicity of some of the second generation
anticoagulants may be inadequate. The dose of vitamin K and
the duration of treatment depends on the type of anticoagulant
ingested and the response of the individual animal. The following
article by the toxicology staff of ADDL addresses some of
the issues of long acting and increased potency anticoagulant
toxicosis.
Ingestion of anticoagulant rodenticidescontinues to be a
common cause of poisoning in small animals. All of these anticoagulants
act by interfering with the vitamin K enzyme complex, which
is responsible for the production of functional clotting factors
II, VII, IX, and X. Following ingestion, the onset of clinical
signs is dependent on the amount ingested, the type of rodenticide,
exposure to other drugs with high protein binding, individual
animal variation, and the depletion of existing amounts of
the affected clotting factors. The amounts of clotting factors
II, VII, IX, and X decrease at rates similar to their half-lives
which range from 6.2
to 41 hours in the dog. Clinical signs relating to a generalized
coagulopathy and hemorrhage usually appear in one to five
days although with internal bleeding the signs may go unnoticed
until later.
It is important to remember that several types of anticoagulant
rodenticides are in common use. These vary in the amount needed
to cause poisoning, and the duration of effect (which is directly
related to the duration of treatment). The older, first
generation anticoagulants, the coumarins (warfarin and fumarin),
and pindone and valone (indanediones), usually require
multiple ingestions and depress the amounts of clotting factors
for seven to ten days. However, the second generation
coumarins, brodifacoum and bromadiolone, and the indanediones,
diphacinone and chlorophacinone, are long-acting and will
depress the amounts of clotting factors for three to four
weeks. In addition, they generally only require a single
ingestion of the anticoagulant-containing bait. Diagnosis
is based on history of ingestion and/or access to an anticoagulant,
clinical signs relating to hemorrhage, and the results of
blood coagulation testing.
Treatment for all anticoagulant rodenticidetoxicoses is vitamin
Kl with symptomatic and supportive treatment. Vitamin Kl itself
has no direct effect on coagulation. Synthesis of new clotting
factors requires six to 12 hours during which the animal may
require supportive therapy such as blood transfusions. The
dose of vitamin Kl and the duration of treatment depend on
the type of anticoagulant ingested and the response of the
individual animal. Pindone, valone, and the first generation
coumarins (such as warfarin) may only require a dose of vitamin
Kl at 1 ing/kg for five to seven days followed by re-evaluation
of the coagulation status and continued therapy if indicated.
However, the long-acting anticoagulants, brodifacoum,bromadiolone,
diphacinone, and chlorophacinone require 2.5 to 5.0 mg vitamin
Kl/kg for three to four weeks followed by re-evaluation of
the coagulation status and possible continuation of vitamin
Kl therapy. More detailed discussions of the mechanisms,
diagnosis, and therapy of anticoagulant rodenticide poisoning
can be found in the references.
SUMMARY: Animals can be poisoned by short-acting or long-acting
anticoagulant rodenticides. Clinical signs relating to
hemorrhage can appear in approximately one to five
days. Diagnosis is based on history, clinical signs and results
of blood coagulation tests. Treatment consists of symptomatic
and supportive therapy and vitamin Kl at a dose and for a
duration of time based on the type of anticoagulant ingested
and the response of the patient
REFERENCES:
Dorman, David C. Anticoagulant, cholecalciferol,
and bromethalin-based rodenticides. In, Veterinary Clinics
of North America: Small Animal Practice,
Beasley, Val Richard, ed.W.B.Saunders Co, Philadelphia,
pp. 339-352, 1990.
Mount, M.E., Woody, B.J., and Murphy, M.J. The
anticoagulant rodenticides. In, Current Veterinary Therapy
DC, Small Animal Practice, R.W, Kirk, ed. W.B. Saunders Co.,
Philadelphia, pp. 156-165, 1986.
- ADDL Toxicology Personnel:
Christina Wilson, Laboratory Technician
Jennifer McCarthy, Assistant Chemist
Robert Everson,PhD, Analytical Chemist,
Laboratory Supervisor Stephen B.Hooser,DVM, PhD,
Veterinary
Toxicologist, Section Head
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