FTY720 is a novel immunomodulator to be developed for use in organ transplantation. The primary objective of this study was to measure safety, single-dose pharmacokinetics, and pharmacodynamics in stable renal transplant patients-the first human use of FTY720. This study used a randomized, double-blind, placebo-controlled design that explored single oral doses of FTY720 from 0.25 to 3.5 mg in 20 stable renal transplant patients on a cyclosporine-based regimen. Safety assessments and blood samples were taken predose and at multiple time points during a 96-h period postdose. Standard pharmacokinetic parameters were derived from the FTY720 whole blood concentrations, measured by HPLC/MS/MS. FTY720 was well tolerated, with no serious adverse events. Transient, asymptomatic bradycardia occurred after administration in 10 of 24 doses of FTY720. Pharmacokinetics are characterized by a prolonged absorption phase; the terminal elimination phase started 36 h after the administration, with elimination half-life (t(1/2)) ranging from 89 to 157 h independent of dose. Maximum plasma concentration and AUC were proportional to dose with low intersubject variability, the apparent volume of distribution (V(d)/F) ranged from 1116 to 1737 L. FTY pharmacodynamics were characterized by a reversible transient lymphopenia within 6 h, the nadir being 42% of baseline. The lymphocyte count returned to baseline within 72 h in all dosing cohorts except the highest. Single oral doses of FTY720 ranging from 0.25 to 3.5 mg were well tolerated and caused a reversible selective lymphopenia. Transient, but asymptomatic bradycardia was the most common adverse event. The long t(1/2) suggests less frequent dosing intervals. The size of V(d)/F is in excess of blood volume, consistent with widespread tissue distribution
