A case of insulin allergy successfully managed using multihexamer‐forming insulin degludec combined with liraglutide

Background Insulin allergy, one of insulin's adverse effects, is rare, especially in patients with Type 2 diabetes, but management is difficult and no effective strategy has yet been established. We experienced an insulin allergy case successfully managed with a novel combination of insulins. Case report A 38‐year‐old woman started insulin therapy when diabetes was diagnosed at age 19 years. Despite poorly controlled diabetes because of poor adherence, she hoped to conceive a child and continuous subcutaneous insulin infusion was introduced using insulin aspart at age 32 years. One month thereafter, she developed skin reactions at the subcutaneous insulin infusion catheter insertion site. The patient was then tested for all rapid‐acting insulin formulations, all of which triggered local reactions. She decided to continue the continuous subcutaneous infusion of human regular insulin, accompanied by oral cetirizine hydrochloride and betamethasone valerate ointment. The patient was admitted to our hospital at age 38 years with high HbA1c levels. She was tested for all long‐acting insulin analogues. All results, except for insulin degludec, were positive. She discontinued continuous subcutaneous insulin infusion and switched to insulin degludec combined with liraglutide. The allergic reactions had completely disappeared and her blood glucose was well controlled by the time of discharge. Conclusion Our patient was allergic to all insulin formulations except insulin degludec. Her allergic reactions completely disappeared after switching to insulin degludec. The crystallized structure of this insulin might mask its skin allergen antigenicity. Furthermore, her postprandial hyperglycaemia was successfully controlled with liraglutide. We propose multihexamer‐forming ultra‐long‐acting insulin plus glucagon‐like peptide‐1 analogues as a therapeutic option for patients with insulin allergy. What's new? We describe a case of a patient who was allergic to all commercially available insulin formulations except insulin degludec. The allergic reactions completely disappeared after switching to insulin degludec. The crystallized structure of insulin degludec might mask its antigenicity as a skin allergen. Postprandial hyperglycaemia was successfully controlled with glucagon‐like peptide‐1 receptor agonist liraglutide. Insulin degludec plus liraglutide may be a therapeutic option in patients with insulin allergy.