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Aim: It has been reported that the pharmacokinetics of cyclosporin A (CsA) in children is different from that in adults. It appears that, in general, pediatric patients metabolize CsA more rapidly than adult patients, necessitating the use of higher dose of the drug in pediatric transplant recipients. In this context, we speculated that single-dose daily administration of low-dose CsA may be associated with a higher peak blood level without associated trough blood level elevation, and thereby yield better results and allow safer use of the drug than the conventional twice daily administration dosing used for the treatment of childhood idiopathic nephrotic syndrome (INS). Methods: A total of 10 children with steroid-dependent relapsing INS (9 with biopsy-proven minimal-change disease) who showed steroid toxicity were enrolled in the study. The initial daily dose of CsA (Neoral) used was around 2.0 mg/kg, given as a single daily dose before breakfast. The dose was subsequently adjusted to achieve a C1-C2 point blood level between 600 - 800 ng/ml. The dose of the concomitantly administered prednisolone was tapered following the commencement of CsA. Results: The mean daily CsA dosage, the mean C1-C2 point blood level and the mean trough blood level in the subjects were 2.2 ± 0.8 mg/kg, 754.0 ± 71.9 nglml and 42.7 ± 29.2 nglml, respectively. At the latest observation, after a mean duration of 17 months (6-24 months) of CsA therapy, the minimum dose of prednisolone required for maintenance of clinical remission and the calculated relapse rate were significantly decreased as compared to the respective pretreatment values (0.52 ± 0.46 mg/kg on alternate days, vs. 0.97 ± 0.63 mg/kg on alternate days, and 0.28 ± 0.32 times per six months, vs. 1.06 ± 0.41 times per six months, respectively, p = 0.005). No significant change was observed in the mean estimated GFR value as compared to the pretreatment value (183.1 ± 35.4 ml/min/1.73m² vs. 185.4 ± 39.3 ml/min/1.73 m²). No evidence ofCsA nephrotoxicity was observed in a repeat renal biopsy performed around 12 months after the commencement of CsA therapy in two patients. Conclusions: Despite the limitations of the study, our results suggest that administration of low-dose CsA as a single daily dose with C1-C2 point blood level monitoring might be an equally effective and safe and, therefore, more cost-beneficial, protocol for the treatment of steroid-dependent cases of relapsing iNS, as conventional twice-daily administration of CsA with trough blood level monitoring. Further studies to confirm the long-term efficacy and safety of this CsA treatment protocol in larger numbers of patients are, however, needed. [ABSTRACT FROM AUTHOR]