Purpose: To determine whether angiotensin-converting enzyme (ACE) inhibition with captopril reduces the progression of microalbuminuria to overt proteinuria in normotensive patients with insulin-dependent diabetes mellitus (IDDM).
Patients and methods: This study was a prospective randomized, double-blind, placebo-controlled trial involving 26 centers in the United States and Canada. One hundred forty-three subjects, 14 to 57 years of age, with IDDM for 4 to 33 years, blood pressure < 140/90 mm Hg in the absence of antihypertensive therapy, and persistent albumin excretion 20 to 200 micrograms/min were randomized to double-blind treatment with captopril 50 mg or placebo BID. Albumin excretion rate (AER), blood pressure, and glycohemoglobin were determined every 3 months, and creatinine clearance (CrCl) and urea excretion were measured every 6 months.
Results: Within 24 months, 6.0% (4/67) of captopril-treated subjects and 18.6% (13/70) of placebo-treated subjects progressed to clinical proteinuria, defined as AER > 200 micrograms/min and at least 30% above baseline (risk reduction = 67.8%, P = 0.037). AER increased at an annual rate of 11.8% (95% confidence interval [CI] -3.3% to 29.1%) in the placebo group, while it declined by 17.9% (CI -29.6% to -4.3%) in the captopril group (P = 0.004). CrCl decreased by 4.9 mL/min per 1.73 m2 per year in the placebo group, while it remained stable in the captopril group (0.9 mL/min per 1.73 m2 per year, P = 0.039 between groups). Ten subjects required treatment for hypertension; 8 in the placebo group and 2 in the captopril group. There was little correlation between the 24-month changes in mean arterial blood pressure and AER in either group. Glycohemoglobin and urinary urea excretion did not differ between groups.
Conclusions: After 24 months of therapy with captopril, compared with placebo, normotensive subjects with IDDM experienced significantly less progression of microalbuminuria to clinical proteinuria, reduced albumin excretion, and preserved CrCl rate. The ACE inhibitor, captopril, was well tolerated.