Colchicine concentration in leukocytes of patients with familial Mediterranean fever

Free and total plasma, granulocyte and mononuclear cell colchicine concentrations were measured by radioimmunoassay in 30 patients with familial Mediterranean fever treated with colchicine 0.5 to 2 mg day-1. Colchicine concentrations showed a large intersubject variability in plasma (0.13-1.75 ng ml-1), granulocytes (4 to 64 ng/10(9) cells), and mononuclear cells (11.4 to 57.6 ng/10(9) cells). Whereas unbound and total plasma colchicine concentrations were well correlated, no correlation was found between total or free plasma and granulocyte or mononuclear cell colchicine concentrations and dose of administered colchicine. In contrast, total or free plasma and granulocyte or mononuclear cell colchicine concentrations were correlated using a hyperbolic function indicating saturable colchicine distribution in both leukocyte populations.