Disposition of minoxidil in patients with various degrees of renal function

The disposition of minoxidil was evaluated after a 5 mg oral dose in 24 subjects with various degrees of renal function. Patients were divided into four groups based on a 24-hour ambulatory creatinine clearance (Clcr): Group I (n = 6) Clcr greater than 90 mL/min, Group II (n = 6) Clcr 50-80 mL/min, Group III (n = 5) Clcr of 30-49 mL/min, and Group IV (n = 7) Clcr less than 30 mL/min. Blood and urine samples obtained over 36 hours were analyzed for minoxidil by a high pressure liquid chromatography technique. Maximum plasma concentration (Cmax) and time to reach Cmax did not differ among the four groups. The terminal elimination half-life was prolonged in Group IV subjects (8.87 +/- 6.12 hours) (mean +/- SD) compared to those in Groups I, II and III (1.38 +/- 0.16, 1.99 +/- 0.45 and 2.42 +/- 0.53 hours, respectively). Apparent total body clearance (Clp/F) decreased as renal function declined; Clp/F = 0.82(Clcr) + 21.8, r = 0.739, P = 0.0001. Renal clearance and apparent nonrenal clearance also were significantly correlated with Clcr. The apparent volume of distribution significantly increased as renal function declined. Thus, the disposition of minoxidil is significantly delayed and dosage adjustment may be necessary in patients with renal insufficiency.