Comparison of effects of enalapril plus hydrochlorothiazide versus standard triple therapy on renal function in renovascular hypertension.

Renal function and antihypertensive drug efficacy were determined in a prospective, double-blind, multicenter study comparing enalapril plus hydrochlorothiazide with standard triple therapy (hydrochlorothiazide, timolol, and hydralazine) in 75 patients with documented renovascular hypertension. Both groups had significant mean decreases in systolic and diastolic blood pressures. Effective control of diastolic hypertension occurred in 96 percent of patients receiving enalapril compared with 82 percent of patients receiving the triple-drug regimen. Effective renal plasma flow was significantly increased by enalapril therapy. In contrast, the glomerular filtration rate had a bimodal response. In 80 percent of enalapril-treated patients, there was no significant change in the inulin clearance, although in 20 percent of patients (10), there was a 28 percent decrease in the inulin clearance with a concomitant 12 percent increase in renal plasma flow. Seven of the 10 patients had unilateral renal artery stenosis, but in all 10, it was high-grade stenosis (more than 80 to 90 percent stenosis). Although a significant rise in the serum creatinine level occurred in one patient in association with diuretic therapy, volume repletion reversed this azotemia. No oliguric acute renal failure occurred in the enalapril-treated group. The cause of the decrease in glomerular filtration rate induced by enalapril plus hydrochlorothiazide in a minority of patients with renal artery stenosis appears to be quite complex. Although the abolishment of the autoregulation of glomerular filtration secondary to blockage of angiotensin II appears to be a primary cause, the roles of decreased arterial pressure, renal counterbalance, concurrent diuretic therapy, and other hemodynamic factors that may maintain glomerular ultrafiltration pressure must also be considered. The results of this study show that enalapril plus hydrochlorothiazide is effective in treating renovascular hypertension. Special care is needed for a small group of patients with renovascular hypertension in whom there is a decrease in the glomerular filtration rate with this therapy. This may identify a subset of patients with unilateral or bilateral high-grade renal artery stenosis in whom alternative therapy--percutaneous angioplasty or surgical intervention--may be considered.