Why should ACE inhibitors be used cautiously in patients with renal artery stenosis?

ACE inhibitors should be used cautiously in patients with renal artery stenosis because they can lead to acute renal failure due to reduced renal perfusion. In cases of renal artery stenosis, there is already a compromised blood flow to one of the kidneys as a result of narrowing. ACE inhibitors work by blocking the conversion of angiotensin I to angiotensin II, leading to vasodilation and a decrease in blood pressure. This mechanism can inadvertently reduce the glomerular filtration pressure in the affected kidney, resulting in inadequate perfusion and potential acute kidney injury.

In patients without renal artery stenosis, the kidneys are typically able to maintain their function despite reduced blood pressure due to the compensatory mechanisms that increase renal perfusion. However, in patients with stenosis, these compensatory mechanisms are compromised. Therefore, careful monitoring and a cautious approach are necessary when prescribing ACE inhibitors to this patient population to prevent serious complications like acute renal failure.