A Case of Fixed Drug Eruption Induced by Inactive Ingredients of Metformin

Abstract

We herein report a 46-year-old man with type 2 diabetes who developed a fixed-drug eruption due to the inactive ingredients of metformin. He was admitted to our hospital due to asthma attack. At that time, he was treated with insulin and vildagliptin/metformin combination tablets. He said that previously, he had developed skin rashes on his lower left thigh and the back of his body after taking metformin. However, eczema did not appear with vildagliptin/metformin combination tablets. Therefore, we switched the vildagliptin/metformin combination tablets to liraglutide and generic metformin tablet (metformin hydrochloride TE^®). Ten days after metformin hydrochloride TE^® prescription, he developed a rash in the same area where the drug eruption caused by metformin had previously appeared. The rash was diagnosed as a fixed-drug eruption. Considering the difference between the metformin combination tablets and metformin hydrochloride TE^®, the allergy was suspected to be induced not by the active ingredients of metformin but by the inactive ingredients of the drug. Subsequently, he tried another generic metformin tablet that did not contain the suspected inactive ingredient (crospovidone). The generic metformin tablet did not induce a fixed-drug eruption. It is important to consider the possibility of drug allergies caused by inactive ingredients.