antivenin, black widow spider (Antivenin (Latrodectus mactans)): Dosing and Uses

Dosing and uses of Antivenin (Latrodectus mactans) (antivenin, black widow spider)

• Adult
• Pediatric

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.