Enalapril versus metoprolol in primary hypertension - effects on the glomerular filtration rate

Background. Hypertension is a significant cause of end-stage renal failure and effective treatment of hypertensive will reduce the progression rate of chronic renal failure in various kidney disorders. Different classes of drugs may be more effective than others in this respect. In this study we compared the effects on the glomerular filtration rate (GFR) of the ACE-inhibitor enalapril and the betablocker metoprolol in patients with mild and moderate primary hypertension during 6 years. Methods. Patients with GFR in the normal range (greater than or equal to 80 ml/min/l.73 m(2) BSA) were included after a placebo treatment period of 4-8 weeks if diastolic blood pressure was 100-120 mm Hg. Target blood pressure was set to <90 mm Hg diastolic. One hundred and thirty patients were randomized in an open parallel study to receive either enalapril or metoprolol. No placebo group was included. GFR was measured using the (CR)-C-51-EDTA clearance method and 81 patients completed the study. Results. At inclusion, there were no significant differences regarding GFR or blood pressure between the groups. The blood pressure treatment goal was reached in all patients and was maintained during the whole observation period. A small but significant fall in GFR by 4 ml/min/1.73 m(2) BSA was noted in both groups after the first year of treatment but thereafter GFR decreased by only 1 ml/min/year/1.73 m(2) BSA, in both groups. Body weight, serum uric acid and triglycerides increased slightly with metoprolol treatment but no other differences between the two treatments were noted. Conclusions. With the blood pressure maintained at the same level using either enalapril or metoprolol during a 6-year study period, GFR decreased to the same extent in the two groups both during the first year and thereafter. The overall magnitude of the GFR decline approached that of the normal age-related decrease of kidney function, i.e. GFR decreased only about 1 ml/min/year. Thus, treatment with an ACE-inhibitor, enalapril, and a beta-blocker, metoprolol, protected the kidney function to the same extent in this 6 year long study in mild and moderate primary hypertension.