Dosing and uses of Antivenin (Latrodectus mactans) (antivenin, black widow spider)
Envenomations
SKIN TEST (ID) FIRST (0.01-0.02 mL diluted 1:10 SC)
IV preferred route: reconstitute one IV vial with NS or D5W (50-100 mL) infuse over 20-30 minutes; may require 2nd dose if there is no response within 1 hour or patient weighs >40 kg
IM administered in anterolateral thigh: 1 vial reconstituted with 2.5 mL of sterile water
Other Indications & Uses
Passive, transient protection from toxic effects of bites by the black widow spider
Additional information
Equine-derived antibodies against venom from Black Widow Spider
Arizona poison control center 520-626-6016 (Tucson)
Treat allergic reactions with corticosteroids (eg, Solumedrol 125 mg IVP), antihistamines, and epinephrine; pretreat if positive skin test
Empiric recommendation: pretreat with diphenhydramine 25 mg IV and start epinephrine (1:1,000) 1mg in 250 mL NS drip at low rate (50 mL/hr) prior to giving antivenom
Pediatric dosage forms and strengths
Envenomation
Skin test
- Antivenom prepared from horse serum; skin or conjunctival sensitivity testing should be performed in all patients prior to treatment
- Infants and neonates: Safety and efficacy not established; for infants, see recommendations for children
- Children and adolescents: 0.02 mL ID test solution (1:10 dilution of normal horse serum in saline), OR
- Instill 1 drop (1:100 of horse serum diluted in normal saline) into the conjunctival sac; itching and reddening of the conjunctiva indicate a positive reaction within 10 minutes
Desensitizing doses
- If test dose positive, give aliquots of 1:100 dilution (0.1 mL, 0.2 mL, then 0.5 mL) and then repeat with the 1:10 dilution by SC injection; wait 30 min in between each aliquot and proceed with next aliquot if no reaction occurs
Treatment
- <12 years: Safety and efficacy of IM injection not established
- Adolescents (IM): 2.5 mL IM in the anterolateral thigh; may give a second dose if necessary
- Neonates and infants (IV): Safety and efficacy not established; for infants, see recommendations for children
- Children and adolescents (IV): Dilute 2.5 mL antivenin in 10-50 mL of 0.9% NaCl; administer IV over 15 min; may give a second dose if necessary
Antivenin (Latrodectus mactans) (antivenin, black widow spider) adverse (side) effects
Frequency not defined
Anaphylaxis
Arthrus reaction
Bronchospasm
Cough
Dyspnea
Edema of face, head, & throat
Fever/chills
Flushing
Hypotension
Pruritus
Rash
Serum sickness within 14 d (75%)
Shock
Urticaria
Vomiting
Wheezing
Warnings
Anaphylaxis to horse serum
Pregnancy and lactation
Pregnancy category: C
Lactation: excretion in milk unknown; use with caution
Pregnancy categories
A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.
B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.
C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.
D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.
X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.
NA: Information not available.
