Patient Allergic to Liraglutide Successfully Switched to Semaglutide Without Reaction

This is a clinical case report. The diagnosis was established through clinical presentation (delayed erythematous plaques at injection sites), allergy testing (to confirm liraglutide as the causative agent), and histopathological study of the affected skin. The patient was subsequently transitioned to semaglutide to assess cross-reactivity.

As GLP-1 receptor agonists are prescribed to millions of people for diabetes and obesity, allergic reactions — though uncommon — will inevitably occur. Clinicians need to know whether a patient allergic to one GLP-1 drug must avoid the entire class or can safely switch to an alternative. This case provides evidence that switching within the class is possible, which is clinically important given the transformative benefits of GLP-1 therapy.

While liraglutide and semaglutide are both GLP-1 receptor agonists, they have different molecular structures — semaglutide has modifications that give it a longer half-life and different pharmacological profile. This structural difference likely explains why the patient tolerated semaglutide despite reacting to liraglutide. As more GLP-1 drugs enter the market (tirzepatide, survodutide, etc.), understanding cross-reactivity patterns will become increasingly important for allergy management.

This is a single case report, so the finding of semaglutide tolerance in a liraglutide-allergic patient cannot be generalized to all patients. Delayed-type hypersensitivity reactions can vary in severity and mechanism between individuals. The specific component of liraglutide causing the reaction (the peptide backbone, fatty acid chain, or excipients) was not definitively identified. Long-term tolerance to semaglutide was not assessed.