# Methimazole Desensitization in a Patient Experiencing a Thionamide-induced Hypersensitivity Reaction

## TL;DR

A patient with a delayed allergic reaction to methimazole was successfully treated with a 27-day desensitization protocol, allowing continued use of the drug.

## Contribution

A novel, individualized desensitization protocol for methimazole in nonimmediate hypersensitivity reactions is presented.

## Key findings

- A 27-day desensitization protocol enabled tolerance of methimazole in a patient with a delayed hypersensitivity reaction.
- The patient showed improvement in thyroid indices following successful desensitization.
- Delayed hypersensitivity reactions to methimazole can be managed with slower desensitization protocols.

## Abstract

Patients with newly diagnosed Graves disease often elect for treatment with the drug methimazole (MMI) over alternative therapies. However, MMI can commonly result in skin allergy that in severe cases can lead to discontinuation of therapy. We present a case of Graves thyrotoxicosis with a delayed hypersensitivity reaction while on MMI. The patient was successfully treated with a novel, individualized, 27-day desensitization protocol that resulted in tolerance of MMI with subsequent improvement in thyroid indices. Previous literature has offered various rapid desensitization protocols to MMI for immediate type hypersensitivity reactions. However, in nonimmediate, delayed hypersensitivity reactions, a slower desensitization protocol can be considered. As demonstrated in this case, desensitization to MMI is a reasonable alternative in patients who wish to avoid definitive therapy who develop an initial adverse reaction to MMI, as this can occur in up to 13% of treated cases.