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