Treat all patients in an emergency department or intensive care setting.
Before a skin test or antivenom administration, insert at least one and preferably two secure intravenous lines.
Perform a skin test for horse serum sensitivity by using a 1:10 dilution of antivenom (some experts prefer this method) or the sample of horse serum provided in the antivenom kit (according to package instructions). Do not perform the skin test unless signs of envenomation are present and imminent antivenom therapy is anticipated. If the skin test is positive, reconsider the need for antivenom as opposed to supportive care, but do not abandon antivenom therapy if it is needed. Even if the skin test is negative, anaphylaxis may still occur unpredictably in rare cases.
If antivenom is used in a patient with horse serum sensitivity, pretreat with intravenous diphenhydramine (See Diphenhydramine) and ranitidine or another H2 blocker (See Cimetidine and Other H2 Blockers), and have ready at the bedside a preloaded syringe containing epinephrine (1:10,000 for intravenous use) in case of anaphylaxis. Dilute the antivenom 1:10 to 1:1000, and administer it very slowly in these cases.
Reconstitute the lyophilized product to 2.5 mL with the supplied diluent, using gentle swirling for 15–30 minutes to avoid shaking and destroying the immunoglobulins (as indicated by the formation of foam).
Dilute this solution to a total volume of 10–50 mL with normal saline.
Administer the diluted antivenom slowly over 15–30 minutes. One or two vials are sufficient in most cases.