Introduction: Angiotensin converting enzyme inhibitors (ACEI) are a common class of medications prescribed to patients for hypertension. Anti-hypertensive use is not normally considered an important factor when treating patients with crotalid envenomations; however, in combination with the venom in this patient, it may have resulted in angioedema.

Case Report: A 65-year-old male on ACEI presented to his community emergency department following a snake envenomation to his thumb. Six vials of Crotalidae polyvalent immune fab were administered, and he was transferred to a referral center. Approximately 18 hours after the envenomation, the patient complained of tongue swelling and difficulty speaking. There was evidence of angioedema, with the right side of the tongue significantly enlarged compared to the left. He was intubated for airway protection and remained on a ventilator for three days. 

Conclusion: Angiotensin converting enzyme inhibitors may potentiate the effects of exogenous bradykinin as some snake venom has naturally occurring bradykinin, which may further amplify its effects. Extra vigilance may be warranted for the development of angioedema in patients receiving ACEI.