The short answer is, it depends. In cats with chronic kidney disease, benazepril has shown to lower blood pressure, including the capillary blood vessel pressure in the filtration system of the kidneys called the glomerulus. At the same time, it increases blood flow through the kidneys and preserves the filtration rate. So it does actually have some benefits for kidney function, which is why it is used.
However, in cats with azotemia, where toxic waste products like BUN and creatinine are elevated on labwork, there is a risk that these levels may increase with benazepril use. Benazepril is typically considered inappropriate to use for cats with acute kidney injury, as from a kidney infection or a toxin, and should likely also not be used in cats with advanced kidney disease.
When azotemia starts to develop on a cat’s bloodwork, we know that about 65% of kidney function has at that point already been lost. However, there might be indicators of earlier kidney insufficiency before bloodwork abnormalities develop, including a dilute urine concentration or protein loss through the urine, that can be monitored for on annual or semi-annual lab work. Benazepril may be most beneficial and safest to use in these cases to address protein loss or hypertension, before azotemia develops.
In the context of how it is metabolized and excreted, benazepril is not very hard on the kidneys at all. It is mostly metabolized and cleared from the body by the liver, with only a smaller percentage by the kidneys. Enalapril by contrast, which is in the same family as benazepril, is excreted almost entirely by the kidneys.