Antivenin (Latrodectus mactans) (antivenin, black widow spider) dosing, indications, interactions, adverse effects, and more

Sections

Sections antivenin, black widow spider
Dosing & Uses
Adverse Effects
Warnings
Pregnancy
Images
Patient Handout
Formulary

Dosing & Uses

AdultPediatric

Dosage Forms & Strengths

powder for injection

6000 Antivenin units

Envenomations

Skin test

Antivenom prepared from horse serum; skin or conjunctival sensitivity testing should be performed in all patients prior to treatment
Intradermal dose: 0.02 mL diluted 1:10; evaluate after 10 min against control test; urticarial wheal surrounded by a area of erythema is considered a positive reaction
Conjunctival test: 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

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

Administration

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

Dosage Forms & Strengths

powder for injection

6000 Antivenin units

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 15-30 min; may give a second dose if necessary

Frequency Not Defined

Anaphylaxis

Arthrus reaction

Bronchospasm

Cough

Dyspnea

Edema of face, head, & throat

Fever/chills

Flushing

Hypotension

Pruritus

Rash

Muscle cramps

Serum sickness within 14 d (75%)

Shock

Urticaria

Vomiting

Wheezing

Contraindications

Hypersensitivity to horse serum

Cautions

Delayed serum sickness may occur 1-2 weeks following administration

Review history and allergies to horse serum containing products; monitor patient closely in a setting where resuscitation can be performed

Use caution in patients with asthma, hay fever or urticaria

Some products may contain thimerosal

Pregnancy & 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.

Images

No images available for this drug.

Patient Handout

A Patient Handout is not currently available for this monograph.

Formulary

FormularyPatient Discounts

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The above information is provided for general informational and educational purposes only. Individual plans may vary and formulary information changes. Contact the applicable plan provider for the most current information.

View explanations for tiers and restrictions

Tier	Description
1	This drug is available at the lowest co-pay. Most commonly, these are generic drugs.
2	This drug is available at a middle level co-pay. Most commonly, these are "preferred" (on formulary) brand drugs.
3	This drug is available at a higher level co-pay. Most commonly, these are "non-preferred" brand drugs.
4	This drug is available at a higher level co-pay. Most commonly, these are "non-preferred" brand drugs or specialty prescription products.
5	This drug is available at a higher level co-pay. Most commonly, these are "non-preferred" brand drugs or specialty prescription products.
6	This drug is available at a higher level co-pay. Most commonly, these are "non-preferred" brand drugs or specialty prescription products.
NC	NOT COVERED – Drugs that are not covered by the plan.

Code	Definition
PA	Prior Authorization Drugs that require prior authorization. This restriction requires that specific clinical criteria be met prior to the approval of the prescription.
QL	Quantity Limits Drugs that have quantity limits associated with each prescription. This restriction typically limits the quantity of the drug that will be covered.
ST	Step Therapy Drugs that have step therapy associated with each prescription. This restriction typically requires that certain criteria be met prior to approval for the prescription.
OR	Other Restrictions Drugs that have restrictions other than prior authorization, quantity limits, and step therapy associated with each prescription.

Medscape prescription drug monographs are based on FDA-approved labeling information, unless otherwise noted, combined with additional data derived from primary medical literature.

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