D2.396 - Successful Desensitization in a Patient with a Delayed Type Hypersensitivity Reaction to Ethambutol

Background: Ethambutol is a key component of treatment regimens for both tuberculosis and atypical mycobacterial infections. Atypical mycobacterial infections often require prolonged and combination drug therapy, limiting alternative options in case of adverse reactions. Although ethambutol is generally well tolerated, hypersensitivity reactions have been described that may lead to discontinuation of treatment. Desensitization is an alternative strategy in selected patients. The aim of this paper is to present a case of successful desensitization to ethambutol in a patient with a delayed-type hypersensitivity reaction.

Methods: A 71-year-old patient was diagnosed with pulmonary infection caused by Mycobacterium Avium complex (MAC) and treatment with azithromycin, ethambutol, rifampicin and amikacin im was initiated. 2 months after the beginning of the treatment, the patient developed an erythematous, pruritic rash localized to the neck, upper chest and upper extremities, while she also developed facial redness with swelling mainly in the eyes and lips. The patient was referred to our department for allergy testing. Initially, a patch test was performed to ethambutol and skin tests to azithromycin and amikacin (negative). We then proceeded to graded drug provocation testing to azithromycin, amikacin and ethambutol in separate days. 9 hours after the completion of ethambutol provocation testing, the patient developed a rash similar to the initial one, while azithromycin and amikacin provocation testing were negative. It was decided to administer ethambutol with a desensitization procedure (12-step protocol), without success. After consultation with the treating pulmonologists, the patient underwent desensitization using a slow protocol (Table 1).

Results: Desensitization was successfully completed and the patient has now completed 12 months of treatment without experiencing adverse reactions while the infection is under control.

Conclusions: Desensitization to delayed-type reactions is feasible and may allow the patient to continue the treatment that is necessary. However, there are no internationally defined protocols and in most cases, individualized protocols are created based on the patient and the drug.