Version May 2024
Envenomation due to Latrodectus mactans; envenomation due to other Latrodectus spp:
Limited data in infants (Ref): Limited data available for some types of envenomations.
Note: The initial dose of antivenin should be administered as soon as possible for prompt relief of symptoms. Delayed antivenin administration may still be effective in treating patients with prolonged or refractory symptoms resulting from black widow spider bites; a case report describes use of antivenin administration up to 90 hours after bite (Ref); however, delayed administration may decrease effectiveness (Ref).
Controlled clinical studies for effectiveness and safety in pediatric patients have not been conducted. Antivenin has reportedly been used successfully in a 2-year-old pediatric patient who experienced black widow spider envenomation (Ref).
If with sensitivity testing a positive reaction to a skin or conjunctival test occurs and antivenin therapy is necessary, pretreat the patient with IV diphenhydramine and an H2 blocker while having a syringe of epinephrine at the bedside.
Infants and Children <12 years: IM; IV (preferred): One vial (2.5 mL); a second dose may be needed in some cases; more than 1 to 2 vials are rarely required.
Children ≥12 years and Adolescents: IM, IV: One vial (2.5 mL); a second dose may be needed in some cases; more than 1 to 2 vials are rarely required.
There are no dosage adjustments provided in manufacturer’s labeling.
There are no dosage adjustments provided in manufacturer’s labeling.
(For additional information see "Black widow spider (Latrodectus mactans) antivenom: Drug information")
Note: The initial dose of antivenin should be administered as soon as possible for prompt relief of symptoms. Delayed antivenin administration may still be effective in treating patients with prolonged or refractory symptoms resulting from black widow spider bites (case report of antivenin administration up to 90 hours after bite (Ref)). However, delayed administration may decrease effectiveness (Ref).
Envenomation due to Latrodectus mactans (black widow spider); envenomation due to other Latrodectus spp. (off-label use) (Ref): If sensitivity testing is performed, a positive reaction to a skin or conjunctival test occurs, and antivenin therapy is necessary, pretreat the patient with intravenous diphenhydramine and an H2-blocker while having a syringe of epinephrine at the bedside: IM, IV: One vial (2.5 mL); a second dose may be needed in some cases; more than 1 to 2 vials are rarely required for rapid resolution of symptoms (Ref).
There are no dosage adjustments provided in manufacturer’s labeling.
There are no dosage adjustments provided in manufacturer’s labeling.
The following adverse drug reactions and incidences are derived from product labeling unless otherwise specified. Frequency not defined.
Dermatologic: Skin rash (rare; associated with hypersensitivity reaction)
Hypersensitivity: Anaphylaxis, hypersensitivity reaction, serum sickness
Neuromuscular & skeletal: Muscle cramps
Concerns related to adverse effects:
• Allergic reactions: May be less frequent than described in initial studies (Clark 2001; Nordt 2012; Offerman 2011). One retrospective study reviewed 163 cases of black widow spider envenomation; 58 patients received antivenin therapy and only 1 case of anaphylaxis occurred (Clark 1992). The risk of reaction appears to be greatest with bolus administration of undiluted antivenin (Clark 2001).
• Delayed serum sickness: Delayed serum sickness, albeit uncommon, may occur 1 to 2 weeks following administration, especially when large doses are used (Clark 2001).
• Horse serum hypersensitivity: Carefully review allergies and history of exposure to products containing horse serum. History of atopic sensitivity to horses may increase the risk of immediate sensitivity reactions. Use with caution in patients with asthma, hay fever, or urticaria; fatal anaphylaxis has been reported in patients with a history of asthma. All patients require close monitoring in a setting where resuscitation can be performed.
Special populations:
• Elderly patients: Due to an increased risk for complications of envenomation, the administration of antivenin may be the preferred initial therapy in patients >60 years of age.
Dosage form specific issues:
• Thimerosal: Some products may contain thimerosal.
Other warnings/precautions:
• Desensitization: A desensitization protocol is available from the manufacturer if sensitivity tests are mildly or questionably positive to reduce risk of immediate severe hypersensitivity reaction. According to the manufacturer, desensitization should be performed when antivenin administration would be lifesaving; however, the risk of anaphylaxis should be weighed against the risks associated with delayed antivenin administration (Rojnuckarin 2009); the risk of allergic reaction may be less frequent than described in initial studies (Clark 2001; Nordt 2012; Offerman 2011).
• Skin/conjunctival test: A skin or conjunctival test may be performed prior to use and a sensitivity testing protocol is provided by the manufacturer; however, the utility of skin and conjunctival tests to accurately identify patients at risk of early (anaphylactic) or late (serum sickness) hypersensitivity reactions to horse-derived antivenins has been questioned (WHO 2005). Normal horse serum (1:10 dilution) is included for sensitivity testing. The absence of a skin or conjunctival hypersensitivity reaction does not exclude the possibility of anaphylaxis or hypersensitivity following antivenin administration. The false-negative rate for skin testing is 10% with similar agents. Conversely, hypersensitivity is not an absolute contraindication in a significantly envenomated patient. Sensitivity testing for antivenom reactions is frequently unreliable with false-positive and false-negative results (Klaewsongkram 2009).
Excipient information presented when available (limited, particularly for generics); consult specific product labeling.
Kit, Injection:
Generic: 6000 Antivenin units
Yes
IM: Administer antivenin into the anterolateral thigh. Apply tourniquet proximal to the injection site if an adverse reaction occurs.
IV: Infuse antivenin over 15 to 30 minutes (Ref). IV administration preferred in severe cases, with shock, or in children <12 years of age. There appears to be no clinical difference in efficacy between the IM and IV route of administration (Ref). If an immediate hypersensitivity reaction occurs, immediately interrupt antivenin infusion and provide appropriate supportive therapy. If administration of antivenin can be resumed after control of the reaction, reinitiate at a slower infusion rate.
IM: Administer antivenin in the anterolateral thigh; apply a tourniquet proximal to the injection site if an adverse systemic reaction occurs.
IV: Administer antivenin over 15 to 30 minutes (Ref); IV administration is preferred in severe cases, with shock. There appears to be no clinical difference in efficacy between the IM and IV route of administration (Ref).
Refrigerate at 2°C to 8°C (36°F to 46°F). Do not freeze.
Pharmacy supply of emergency antidotes: Guidelines suggest that at least 1 vial be stocked in areas with indigenous black widow spiders. Suggested amount is stated to be a sufficient quantity to treat 1 patient weighing 100 kg for an initial 8- to 24-hour period (Dart 2018); actual amount to be stocked should take into account site-specific and population-specific needs.
Treatment of patients with symptoms (eg, cramping, intractable pain, and hypertension that are unresponsive to other therapies [eg, benzodiazepines, opioids]) due to Latrodectus mactans (black widow spider) envenomation (FDA approved in children and adults); latrodectism due to other Latrodectus species found in North America (eg, L. bishopi, L. geometricus, L. hesperus, L. variolus) may be treated with antivenin intended for use in patients envenomed by Latrodectus mactans.
None known.
There are no known significant interactions.
Use during pregnancy (second and third trimester) has been described in case reports; all patients delivered healthy infants (Handel, 1994; Russell, 1979; Sherman, 2000). In general, medications used as antidotes should take into consideration the health and prognosis of the mother; antidotes should be administered to pregnant women if there is a clear indication for use and should not be withheld because of fears of teratogenicity (Bailey, 2003). Treatment of a pregnant patient with antivenom should be considered early in the course of an envenomation and in patients experiencing local, regional, or systemic effects refractory to opioids and/or benzodiazepines (Brown, 2013).
Vital signs; hypersensitivity reactions; serum sickness (for 2 to 3 weeks following administration); worsening of symptoms due to envenomation.
Neutralizes the venom of Latrodectus mactans (black widow spiders), but may also be effective following envenomation by other Latrodectus species (including L. bishopi, L. geometricus, L. hesperus, and L. variolus) (Clark 2001; Isbister 2003).
Onset of action: Within 30 minutes; symptoms of envenomation usually subside after 1 to 3 hours.
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