Optimal Trough Concentration of Tacrolimus in Pediatric Patients With Primary Nephrotic Syndrome

The trough concentration (C₀) of tacrolimus in children with nephrotic syndrome (NS) has rarely been explored, so its target level was based on transplant research. This study aimed to determine the optimal tacrolimus C₀ in NS children. Data from primary NS children treated with tacrolimus at Wuhan Children's Hospital in the last 10 years were retrospectively collected. According to the cutoff C₀ analyzed by receiver-operator characteristics (ROC) analysis, patients were divided into very low- (< 4 ng/mL), low- (4-5 ng/mL), medium- (5-7 ng/mL), and high-concentration (7-10 ng/mL) groups. A total of 196 patients were enrolled for primary outcome analysis. Compared to medium-concentration group, only the very low-concentration group obtained significant inferior primary outcomes, including overall remission rate, relapse-free survival rate, and relapse rate at 6 months. For secondary outcomes, the very low-concentration group experienced more frequent treatment failure in 12 months, whereas the high-concentration group suffered a higher risk of adverse events than the medium-concentration group. For steroid-resistant NS, very low- and low-concentration groups required longer time to achieve remission compared to medium-concentration group. For steroid-sensitive NS, the very low-concentration group suffered a higher relapse frequency than medium-concentration group. Lastly, the dose of tacrolimus required for children with different CYP3A5 genotypes with or without Wuzhi capsules was analyzed. In conclusion, tacrolimus may be targeted to C₀ of 4-7 ng/mL during the first 6 months in children with NS. For steroid-resistant NS, C₀ of 5-7 ng/mL can achieve a rapid remission.