Abstract
Objective: A case of insulin allergy to insulin aspart, insulin aspart protamine/insulin aspart 70/30, insulin lispro, and insulin lispro protamine/insulin lispro 75/25 in a patient with type 2 diabetes mellitus is reported. Case Summary: A 76-year-old Caucasian male weighing 81 kg presented with complaints of burning, lumps, and a rash where his insulin aspart protamine/insulin aspart 70/30 was injected 2 months after initiation. Because poor injection technique can mimic insulin allergy, the patient was counseled again on proper injection technique. The patient presented 2 weeks later with the same complaints. Insulin aspart protamine/insulin aspart 70/30 was discontinued and insulin lispro protamine/insulin lispro 75/25 was initiated. The patient presented 3 months later with a localized reaction. Insulin lispro protamine/insulin lispro 75/25 was discontinued and insulin U100 glargine and insulin lispro were initiated. One week later, the patient still had complaints of a localized reaction and was referred to an allergist for testing. Skin prick tests revealed insulin allergy to insulin aspart and insulin lispro but not to insulin U100 glargine or insulin glulisine. The patient’s regimen was changed to insulin U100 glargine and insulin glulisine, and he has not experienced any reaction since. Discussion: Allergic reactions to human insulin preparations are rare and may present as a localized reaction or a generalized reaction. Different types of allergic reactions to human insulin have been reported, including type I, type III, and type IV hypersensitivity reactions. If insulin allergy is suspected, the following steps should be taken to confirm such allergy: evaluation of injection technique, switching to a different insulin preparation, and referral to an allergist for allergy testing if necessary. Conclusion: A patient with type 2 diabetes mellitus experienced a type I hypersensitivity reaction to insulin aspart, insulin aspart protamine/insulin aspart 70/30, insulin lispro, and insulin lispro protamine/insulin lispro 75/25.