Antivenin (Latrodectus mactans) (Equine)
Class: Antitoxins and Immune Globulins
ATC Class: J06AA
VA Class: IM300
Introduction
Antivenin; equine immunoglobulins capable of neutralizing venom toxins of black widow spiders (Latrodectus mactans).
Uses for Antivenin (Latrodectus mactans) (Equine)
Latrodectus mactans Envenomation
Treatment of symptoms resulting from black widow spider (Latrodectus mactans) bite.
May shorten duration of symptoms and reduce need for hospitalization.
Consultation with experts experienced in treating black widow spider envenomation recommended to guide treatment decisions regarding individual patients.
Antivenin (Latrodectus mactans) (Equine) Dosage and Administration
General
Perform sensitivity testing (skin or conjunctival test) in all patients prior to administration.Desensitization can be attempted in individuals with history of allergy or with mildly or questionably positive sensitivity tests, but only if antivenin is considered necessary to save patient’s life and epinephrine is readily available. (See Sensitivity Testing and Desensitization under Dosage and Administration.)
Negative sensitivity test does not preclude possibility of sensitivity reaction. Monitor closely for immediate sensitivity reactions during administration; monitor for serum sickness for average of 8–12 days after administration. (See Sensitivity Reactions under Cautions.)
Early use advised for prompt relief, but delayed administration (up to 90 hours after envenomation) has accelerated recovery and alleviated manifestations.
Sensitivity Testing and Desensitization
Skin sensitivity test (intradermal): Inject no more than 0.02 mL of the 1:10 dilution of normal equine serum provided by manufacturer; inject equal volume of 0.9% sodium chloride injection on contralateral extremity to serve as control. Observe results after 10 minutes. Positive skin test reaction consists of urticarial wheal surrounded by zone of erythema.
Conjunctival sensitivity test (topical): Place 1 drop of normal equine serum provided by manufacturer (1:10 dilution in adults or 1:100 dilution in children) into conjunctival sac and observe for 10 minutes. Positive conjunctival test usually occurs within 10 minutes and consists of itching of eye and reddening of conjunctiva.
Desensitization procedure (sub-Q): Prepare 1:10 and 1:100 dilutions of the antivenin in separate vials or syringes using 0.9% sodium chloride injection. Inject 0.1, 0.2, and then 0.5 mL of the 1:100 dilution at 15- or, preferably, 30-minute intervals; if there has been no reaction to previous doses, repeat using 1:10 dilution and then with undiluted antivenin. If immediate sensitivity reaction occurs at any time, apply tourniquet proximal to injection sites and administer epinephrine proximal to tourniquet or into another extremity. After at least 30 minutes, may continue desensitization procedure using last dose that did not produce reaction. If no reaction occurs after administration of 0.5 m...
