BACKGROUND: Calcineurin-inhibitors have wide inter-individual variation in drug response. Although therapeutic drug monitoring has been conducted to optimize personalized regimen, toxicity or rejection may occur. In this study, pharmacologic effect was evaluated by measuring calcineurin activity in peripheral blood after administration of a single dose of cyclosporine in healthy volunteers. METHODS: 7 healthy Korean male subjects received cyclosporine 200 mg and blood samples were drawn immediately before and at 1, 1.5, 4, 6, 12 h after dosing to measure calcineurin activity. The blood concentrations of cyclosporine were determined for 24 hours. Calcineurin activity assay was done with Calcineurin cellular activity assay kit (Calbiochem, USA). Frozen whole blood samples in liquid N2 were thawed and lysed with lysis buffer. 50 microL of phosphate standard curve samples were added to each well of a 96-well plate and 10 microL of diluted lysate were added to the well with RII phosphopeptide substrate. After incubating for 30 min, reaction was terminated by adding 100 microL GREEN(TM) reagent. Absorbance was read at 620 nm using spectrophotometer. We evaluated percent change in calcineurin activity from baseline level in relation to the lowest level. RESULTS: Decrease of calcineurin activity was confirmed after cyclosporine administration (mean +/- SD: 58.9 +/- 48.6 (%)). Significant correlation was shown between calcineurin activity change and pharmacokinetic parameters (AUClast: r = 0.834, p value = 0.01, Cmax: r = 0.774, p value = 0.02). CONCLUSION: In this study, we confirmed the pharmacologic effect and its correlation with pharmacokinetics after administration of a single dose of cyclosporine by measuring calcineurin activity in peripheral blood in healthy volunteers.