7
METHOD OF ANTIVENOM ADMINISTRATION
- obtain written, informed consent if possible before giving
- draw up epinephrine in a syringe at bedside, ready for administration in the event of an anaphylactic/-oid
reaction
- skin testing: no clinical benefit (but is recommended by Wyeth for ACP; not recommended for CroFab)
- a "medicolegal procedure"; wastes 20-30 min of time
- test is not 100% accurate:
- a negative test to ACP does not r/o possibility of a hypersensitivity rxn (occurs in approx. 1-10%)
- not all patients who have a positive skin test demonstrate a reaction if given ACP (does not
contraindicate giving antivenom to a patient with a life-threatening envenomation)
-
always be prepared for an anaphylactic reaction in any patient given AV (ACP or CroFab)
- expand intravascular volume with crystalloid if no contraindication (to limit severity of any
anaphylactoid reaction)
- if giving ACP, administer an IV dose of H1 & H2 blockers (e.g. diphenhydramine & cimetidine) prior to beginning
infusion
- dilute antivenom to be given in NS or RL (for CroFab: 250 ml; for ACP: 50-100 ml for each vial to be given;
e.g. 5 vials in 250-500 ml)
- begin the infusion slowly (approx. 15 drops/min) through an IV in an uninjured extremity
- if no reaction over several minutes, increase rate to complete dose in 1 hour
- if a reaction occurs (see below), temporarily stop the antivenom and treat with epi, diphenhydramine,
cimetidine and steroids as needed
SUGGESTED STARTING DOSES
# of Vials
Severity:
CroFab
ACP
nonenvenomation
0
0
mild
4-6
0 or 5 - controversial
moderate
4-6
10
severe/very severe
6
15
- Monitoring Therapy:
- after the initial dose is given, reassess clinical response...
- for CroFab: watch over the next hour... if progression of Ssx/Lab abnormalities, give another 4-6 vials
(and continue in this fashion until stable); then give 2 more vials q6h x 3 additional doses (these dosage
recommendations may change as more experience is gained with this product)
- for ACP: if swelling or systemic Ssx progress or recur, give 1-5 more vials q 30 min - 2 hr prn (very severe
envenomations may require 20-30 vials); keep ACP levels high for first 4 hr
- with adequate antivenom:
- swelling/erythema will quickly begin to reverse
- patient subjectively improves (decreased pain)
-
systemic
Ssx's
improve (e.g. bleeding, GI sx's)
- normalization of vital signs and urine output
- fasciculations may disappear
- better to err on side of overtreatment than undertreatment
- children require at least an adult starting dose (due to decreased resistance to venom); adjust volume of
diluent as needed
- benefits generally outweigh risks in pregnancy (pitviper venom poisoning known to cause fetal demise)
- MANAGEMENT OF THE PATIENT WITH AN ALLERGY TO ANTIVENOM AND A SEVERE
ENVENOMATION:
- if starting with ACP, switch to CroFab if available
- can still usually give ACP if no patient is severely envenomed and no CroFab available
- consult a specialist (allergist or expert in snake envenomations)
