Observational study of the clinical utility of sulfamethoxazole serum level monitoring in the treatment of brain abscesses due to Nocardia species

Although there is a lack of data in trimethoprim-sulfamethoxazole (TMP-SMX) serum monitoring utility for invasive nocardial infections, therapeutic drug monitoring is widely used to optimize dosing and avoid adverse reactions that may cause treatment interruption. We retrospectively reviewed all adults who received TMP-SMX to treat nocardial brain abscess and had SMX serum level testing from 2010 to 2020. Twenty-two patients received treatment with TMP-SMX for Nocardia species brain abscess and 16 (72.7%) had a reported SMX level, with a median patient age of 65.5 years (interquartile range, IQR 59.5–72.5). Compared to those who did not have a documented SMX serum level, patients with SMX levels had a shorter median course of TMP-SMX treatment (322 days [IQR 188–365] vs. 365 [IQR 224–365]; P = .31) and higher therapeutic induction dose (10 [62.5%] vs. 3 [50%]; P = .92). Similarly, they were more frequently on hemodialysis (3 [13.6%] vs. 1 [4.5%]; P = > .99). The median peak level was 158.5 (IQR 120–218) μg/mL, collected at 2 hours (75%) post-administration in the induction phase (81.3%). Patients with documented SMX levels had fewer reported drug toxicity (5 [31.3%] vs. 4 [66.7%]; P = .1) than those without SMX levels. Among the five patients who reported TMP-SMX-related toxicity, 4 (80%) had an SMX peak level >150 μg/mL. There was no difference in the cure, relapse, and death rates among the two groups. While SMX level was not associated with Nocardia species brain abscess cure rates and mortality, most patients with SMX peak >150 μg/mL experienced drug toxicity.