To determine the cyclosporine trough (C0) and two-hour post-dose concentrations (C2) in children with nephrotic syndrome (NS) and study the factors influencing them.

In this ambispective cohort study, children with NS (including frequently relapsing, steroid-dependent and steroid-resistant nephrotic syndrome) on cyclosporine therapy were enrolled. Clinical and laboratory data were recorded. C0 and C2 were estimated using liquid chromatography mass spectrometry.

Among 27 patients with a mean (SD) age of 6.4 (4.1) years, the median (Q1, Q3) of C0 and C2 were 114.8 (86.1, 186.3) ng/mL and 661.6 (442.1, 884.6) ng/mL, respectively. At a mean (SD) cyclosporine dose of 4.1 (0.8) mg/kg/day, 12 (44%) patients had C0 above and 4 (15%) below the therapeutic range (80–120 ng/mL). C2 levels were outside the recommended ranges in 17 (63%) children, within range in 7 (26%), and below in 3 (11%). Capsule users had higher C0 than syrup users. Amlodipine therapy was associated with higher C0 levels.

Nearly half the children had C0 and C2 levels outside the therapeutic range. Dosage form and amlodipine influenced C0, not C2 concentrations.