TOPLINE:

Among adult inpatients labeled as having a low-risk sulfa antibiotic allergy, 99% tolerated an oral challenge with trimethoprim-sulfamethoxazole, according to a prospective study.

METHODOLOGY:

• The study included 76 adult inpatients who reported having a sulfa antibiotic allergy (median age, 67 years; 58% female), 30 of whom were immunocompromised.
• Patients were at lower risk from an allergic reaction, based on a score < 3 on the Antibiotic Allergy Assessment Tool or the SULF-FAST clinical decision rule.
• Patients received a single-dose trimethoprim-sulfamethoxazole direct oral challenge and were monitored for 90 days post-challenge.

TAKEAWAY:

• Overall, 99% of patients tolerated the direct oral challenge, while one patient experienced a delayed exanthem, which was managed with an antihistamine.
• In the 90 days after the challenge, 22% of patients utilized trimethoprim-sulfamethoxazole.
• Patients who were immunocompromised were more likely to use the medication after the challenge (adjusted odds ratio, 5.6; 95% CI, 1.3-23.0).

IN PRACTICE:

“Unlike penicillin allergy, trimethoprim-sulfamethoxazole is a drug more commonly associated with severe cutaneous adverse reactions, and education around risk assessment, including identifying noncutaneous features of severe cutaneous adverse reactions such as organ dysfunction, is required to ensure only low-risk phenotypes undergo [direct oral challenge],” the authors of the study wrote.

SOURCE:

Elise A. Mitri, with the University of Melbourne, Melbourne, Australia, was the corresponding author of the study, which was published online on February 2, 2026, in Infection Control & Hospital Epidemiology.

LIMITATIONS:

The study had a relatively small sample size and predominantly included patients with a SULF-FAST score of 0-1, possibly limiting the generalizability of the findings to patients with higher risk scores.

DISCLOSURES:

The study was supported by a PhD scholarship from the National Allergy Centre of Excellence (Australian Government), as well as by the Victorian Government’s Operational Infrastructure Support program and the National Health and Medical Research Council Emerging Leadership Fellowship. The authors declared having no conflicts of interest.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.