Page 494 - Clinical Small Animal Internal Medicine

462 Section 5 Critical Care Medicine

Diagnosing coral snake envenomation is complicated species if possible. Because the effectiveness of antivenin
VetBooks.ir by the lack of local tissue reaction and the fact that signs is dependent on binding circulating venom molecules, a
molar dosing regimen is followed, meaning that the
may not develop for up to 12 hours following envenoma-
tion. Any patient exhibiting signs of a rapidly progressive
ascending paralysis in coral snake endemic areas should dose of antivenin is dependent on the volume of venom
injected rather than the patient’s body size. In fact,
be considered at risk and be treated appropriately. smaller animals often require higher doses of antivenin
Owners may not be as aware of coral snake exposure due due to differences in the volume of distribution of venom
to the smaller size of the snakes and the lack of a warning in a small versus large dog. Antivenin therapy is most
system such as a rattle. effective when instituted early in the disease course
although it is effective as long as circulating venom is
present and should be considered even many hours
Therapy after an envenomation if clinical signs are severe or pro-
gressive or if a coagulopathy develops.
First Aid Unfortunately, the cost of antivenin therapy can be
quite high and often results in patients receiving less
Appropriate veterinary care should not be delayed to antivenin than ideal circumstances would dictate. When
allow first aid measures to be performed. First aid for faced with the predicament of whether or not to admin-
snake bites has a long and storied past, including lancing ister a dose of antivenin with the belief that it will not be
and suctioning the wound, placing tourniquets, ice pack- a completely effective dose, the clinician should err on
ing, warm packing, and administering electroshock, the side of treatment since binding even a portion of the
among other techniques. To date, none of these meas- free venom may improve the clinical course.
ures has demonstrated any improvement in outcome; in There are currently two major types of antivenin com-
fact, some can significantly worsen the clinical course of mercially available. Polyvalent whole molecule antivenin
disease. Placement of tourniquets may exacerbate the is derived from the serum of horses sensitized to several
amount of tissue injury by preventing dilution of the North, Central, and South American pit viper species
venom as it is distributed throughout the body and pro- and contains the entire IgG antibody and may contain
longing the duration of time that venom is present in equine albumin, depending on manufacturer. The sec-
the affected tissue bed. Envenomation that would not ond type of antivenin is composed of the F ab portion only
otherwise induce tissue necrosis might therefore result of an ovine‐ or equine‐derived antibody rather than the
in massive tissue loss if a tourniquet is placed inappropri- complete immunoglobulin molecule. Whole immuno-
ately in the field. Cold packing can induce local vasocon- globulin antivenin is generally less expensive and more
striction and exacerbate tissue injury through a similar readily available than F ab ‐based antivenins but due to the
mechanism. Incision and suction should never be per- presence of the entire IgG molecule and possibly addi-
formed. It is not likely to result in any improvement in tional foreign proteins (equine or ovine albumin), the
outcome and may put the care provider at risk. The best possibility of hypersensitivity reaction is increased.
first aid measure available is to immobilize the affected Antivenins containing the smaller F ab portion of the
area if possible and to transport the patient to the nearest immunoglobulin molecule are less immunogenic and
veterinary facility capable of treating snake bite. Due to may be better able to diffuse into damaged tissue due to
the preponderance of snake bites being located on the their smaller size. However, this smaller size results in a
head and muzzle of dogs and cats, immobilization is not shorter elimination half‐life than the larger complete mol-
often feasible and rapid transport is the best option. ecule antivenins. This can lead to a situation in which the
While first aid measures in necrogenic snake bites do antivenin is eliminated more rapidly than it is capable of
not include application of a tourniquet or compression binding circulating venom molecules, resulting in recur-
bandage, coral snake envenomations do benefit from rence of clinical signs. If using an F ab ‐based antivenin, the
constriction. There is very little local tissue injury associ- clinician should be aware of this possibility and recog-
ated with coral snake envenomations, meaning the appli- nize the fact that repeated dosing may be needed every six
cation of a tight compression bandage on the affected hours to most effectively treat the patient.
area should be performed if possible. While the F ab ‐based antivenins are less immunogenic
than the whole molecule formulations, both types of
antivenin are capable of causing immediate and delayed
Antivenin Therapy
immune reactions, with a reported incidence of 5–13%.
Regardless of the primary effect of the venom, the main- Anaphylactic (type I) or anaphylactoid hypersensitivity
stay of treatment for snake bite is the administration of reactions occur immediately upon administration of
venom antibodies (antivenin) specific to the envenoming antivenin, are dose related and are due to either an