The degree of renal impairment was defined according to baseline creatinine clearance (CrCl) (normal renal function when CrCl > 80 ml/ min; mild impairment with CrCl = 50-79 ml/ min; moderate impairment with CrCl = 30-49 ml/ min and severe impairment with CrCl = 10-29 ml/ min).