| Summary: | Renin-angiotensin-aldosterone system (RAAS) inhibition exerts a renoprotective effect independent of blood pressure reduction. Many studies using an end-point of proteinuria compared the effects of angiotensin-converting enzyme inhibitor (ACE-I) or angiotensin receptor blocker (ARB) monotherapy with combination ACE-I/ARB therapy. Despite methodological limitations, most studies suggest that combination therapy provides a greater antiproteinuric effect than monotherapy, perhaps because of more prolonged and complete RAAS inhibition. COOPERATE and ONTARGET used more robust end-points to study renoprotective effects. In COOPERATE, combination therapy resulted in significantly longer times to doubling serum creatinine or developing end-stage renal disease than trandolapril or losartan monotherapy. However, a secondary ONTARGET finding was that combination therapy significantly increased the risk for renal dysfunction compared with ramipril or telmisartan alone. Eventually, the VA NEPHRON-D trial should provide definitive data relating to patients with diabetic nephropathy. Results of AVOID suggest the renoprotective benefits of combination therapy extend to the direct renin inhibitors (DRI). In AVOID, combination therapy with aliskiren, a DRI, and losartan resulted in 20% greater protein excretion decrement than losartan monotherapy. Future trials should examine higher RAAS inhibitor doses, facilitate differentiation of renoprotective and antihypertensive effects of RAAS blockade, and use end-points that robustly demonstrate renoprotective effects.
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