RAPID DESENSITIZATION TO TRIMETHOPRIM-SULFAMETHOXAZOLE IN FIXED DRUG ERUPTION: WHAT TO DO IF IT FAILS?

Fixed drug eruption (FDE) accounts for around 2-3% of cutaneous drug reactions in adults and can progress to bullous fixed drug eruption, which carries a worse prognosis. Desensitization is a safe and effective management tool that can be tailored to various durations, ranging from rapid one-day protocols to extended periods lasting several days. A 64-year-old male patient with liver cirrhosis was diagnosed with brucellosis during his pre-transplant evaluation. Trimethoprim-sulfamethoxazole (TMP/SMX) was prescribed, but after 24 hours, he developed FDE on the abdomen, foot , and base of the penis, requiring its discontinuation. After the transplant , the need to administer TMP/SMX as a prophylactic antibiotic , pending the infectious disease specialist's order, led to its reintroduction through an 11-step, 3-hour rapid desensitization, which resulted in a recurrence of FDE after 8 hours. Topical steroid treatment was indicated with improvement of symptoms. Subsequently, a prolonged 11-step, 11-day desensitization was performed (Figure 1), achieving tolerance to the medication and allowing its continuous prophylactic use. The patient had no further adverse reactions in the following four months. FDE can be managed through desensitization in cases where alternative agents are not an option. Although multiple desensitization protocols for delayed HSRs to TMP-SMX have been conducted over hours, days, or weeks, no standardized protocol exists. However, in cases of failed rapid desensitization, a more prolonged approach can be successful, enabling the continuation of first-line prophylactic treatment.