Do we pretreat with medications such as antihistamines (e.g. diphenhydramine) and corticosteroids (e.g. hydrocortisone) before administering scorpion antivenom?

Pretreatment for Scorpion Antivenom Administration

Routine premedication before scorpion antivenom administration is not recommended as it is usually unnecessary due to the relatively low risk of systemic reactions with scorpion antivenom. 1, 2

Evidence on Scorpion Antivenom Reactions

• Scorpion antivenom has a relatively low incidence of systemic reactions compared to other antivenoms, with only about 8% of patients experiencing immediate hypersensitivity reactions, which are generally mild 2
• Unlike rush immunotherapy with aeroallergens (which has high reaction rates of up to 73%), rush protocols for Hymenoptera venom immunotherapy have not been associated with similarly high incidence of systemic reactions 1
• The same principle applies to scorpion antivenom, which follows a similar safety profile to other venom immunotherapies 1, 2

When Premedication Should Be Considered

• Premedication may be considered for patients with:
  • History of previous anaphylactoid reactions to any antivenom 1, 3
  • History of severe allergic reactions to medications or biologics 1
  • Patients with asthma, atopic conditions, or those receiving β-adrenergic blocking agents 1, 3

Premedication Protocol (If Needed)

If premedication is deemed necessary based on individual risk assessment:

Standard Protocol (When Time Permits):

• Prednisone 50 mg orally at 13 hours, 7 hours, and 1 hour before antivenom administration 1, 3
• Diphenhydramine 50 mg orally or intramuscularly 1 hour before antivenom administration 1, 3

Emergency Protocol (When Immediate Treatment Required):

• Hydrocortisone 200 mg intravenously immediately and every 4 hours until antivenom administration 1, 3
• Diphenhydramine 50 mg intramuscularly 1 hour before antivenom administration 1, 3

Important Considerations

• Premedication does not guarantee prevention of anaphylaxis - patients can still experience life-threatening reactions despite pretreatment 1
• Low-dose adrenaline (0.25 ml of 1:1000 solution subcutaneously) immediately before antivenom has shown efficacy in preventing severe reactions to snake antivenom and may be considered in high-risk cases 4
• Adding hydrocortisone to adrenaline may negate the beneficial effects of adrenaline in preventing reactions 4
• Patients receiving β-adrenergic blocking agents may require more intensive and prolonged treatment if reactions occur 1

Monitoring and Management

• All patients receiving antivenom should be monitored for at least 30 minutes after administration, regardless of premedication status 1
• Epinephrine should be immediately available for treatment of anaphylaxis 1
• For patients with severe previous reactions, closer monitoring (up to 6 hours) may be warranted 1

Conclusion

While premedication is commonly used before administration of other antivenoms and contrast media, the evidence does not support routine premedication before scorpion antivenom due to its relatively low risk of causing systemic reactions. Premedication should be reserved for patients with specific risk factors for anaphylaxis.