Renal Effects of Aliskiren Compared With and in Combination With Irbesartan in Patients With Type 2 Diabetes, Hypertension, and Albuminuria

OBJECTIVE

We investigated whether the antiproteinuric effect of the direct renin inhibitor aliskiren is comparable to that of irbesartan and the effect of the combination.

RESEARCH DESIGN AND METHODS

This was a double-blind, randomized, crossover trial. After a 1-month washout period, 26 patients with type 2 diabetes, hypertension, and albuminuria (>100 mg/day) were randomly assigned to four 2-month treatment periods in random order with placebo, 300 mg aliskiren once daily, 300 mg irbesartan once daily, or the combination using identical doses. Patients received furosemide in a stable dose throughout the study. The primary end point was a change in albuminuria. Secondary measures included change in 24-h blood pressure and glomerular filtration rate (GFR).

RESULTS

Placebo geometric mean albuminuria was 258 mg/day (range 84–2,361), mean ± SD 24-h blood pressure was 140/73 ± 15/8 mmHg, and GFR was 89 ± 27 ml/min per 1.73 m². Aliskiren treatment reduced albuminuria by 48% (95% CI 27–62) compared with placebo (P < 0.001), not significantly different from the 58% (42–79) reduction with irbesartan treatment (P < 0.001 vs. placebo). Combination treatment reduced albuminuria by 71% (59–79), more than either monotherapy (P < 0.001 and P = 0.028). Fractional clearances of albumin were significantly reduced (46, 56, and 67% reduction vs. placebo). Twenty-four-hour blood pressure was reduced 3/4 mmHg by aliskiren (NS/P = 0.009), 12/5 mmHg by irbesartan (P < 0.001/P = 0.002), and 10/6 mmHg by the combination (P = 0.001/P < 0.001). GFR was significantly reduced 4.6 (95% CI 0.3–8.8) ml/min per 1.73 m² by aliskiren, 8.0 (3.6–12.3) ml/min per 1.73 m² by irbesartan, and 11.7 (7.4–15.9) ml/min per 1.73 m² by the combination.

CONCLUSIONS

The combination of aliskiren and irbesartan is more antiproteinuric in type 2 diabetic patients with albuminuria than monotherapy.Albuminuria is the best available surrogate parameter in the treatment of diabetic nephropathy. Degree of proteinuria is associated with risk of renal and cardiovascular events (1). Proteinuria reduction is associated with a slowing of the decline in renal function (2). Blockade of the renin-angiotensin-aldosterone system (RAAS) is the cornerstone treatment of incipient and overt diabetic nephropathy, and in type 2 diabetes angiotensin II receptor blockers (ARBs) such as irbesartan are considered standard treatment after the Irbesartan in Patients with Type 2 Diabetes and Microalbuminuria (IRMA) 2 Study (3) and Irbesartan Diabetic Nephropathy Trial (IDNT) (1).Aliskiren represents a new principle of blocking the RAAS, inhibiting renin directly and acting at the rate-limiting step. The drug is approved for treatment of hypertension but has also shown renoprotective potential in patients with type 2 diabetes and albuminuria (4,5).Combining an ARB and a direct renin inhibitor could offer improved RAAS blockade by acting both at the receptor level and at the first step of the cascade. We compared the antiproteinuric effect of maximal recommended doses of aliskiren, irbesartan, and the combination in patients with type 2 diabetes and albuminuria. We also assessed the impact of the treatments on RAAS components and biomarkers of inflammation, endothelial dysfunction, and cardiovascular risk.