Background: Renal function declines progressively in patients who have diabetic nephropathy, and the decline may be slowed by antihypertensive drugs. The purpose of this study was to determine whether captopril has kidney-protecting properties independent of its effect on blood pressure in diabetic nephropathy.

Methods: We performed a randomized, controlled trial comparing captopril with placebo in patients with insulin-dependent diabetes mellitus in whom urinary protein excretion was > or = 500 mg per day and the serum creatinine concentration was < or = 2.5 mg per deciliter (221 mumol per liter). Blood-pressure goals were defined to achieve control during a median follow-up of three years. The primary end point was a doubling of the base-line serum creatinine concentration.

Results: Two hundred seven patients received captopril, and 202 placebo. Serum creatinine concentrations doubled in 25 patients in the captopril group, as compared with 43 patients in the placebo group (P = 0.007). The associated reductions in risk of a doubling of the serum creatinine concentration were 48 percent in the captopril group as a whole, 76 percent in the subgroup with a baseline serum creatinine concentration of 2.0 mg per deciliter (177 mumol per liter), 55 percent in the subgroup with a concentration of 1.5 mg per deciliter (133 mumol per liter), and 17 percent in the subgroup with a concentration of 1.0 mg per deciliter (88.4 mumol per liter). The mean (+/- SD) rate of decline in creatinine clearance was 11 +/- 21 percent per year in the captopril group and 17 +/- 20 percent per year in the placebo group (P = 0.03). Among the patients whose base-line serum creatinine concentration was > or = 1.5 mg per deciliter, creatinine clearance declined at a rate of 23 +/- 25 percent per year in the captopril group and at a rate of 37 +/- 25 percent per year in the placebo group (P = 0.01). Captopril treatment was associated with a 50 percent reduction in the risk of the combined end points of death, dialysis, and transplantation that was independent of the small disparity in blood pressure between the groups.

Conclusions: Captopril protects against deterioration in renal function in insulin-dependent diabetic nephropathy and is significantly more effective than blood-pressure control alone.