Much of the information promoting use of ACE inhibitors in cats with renal disease comes from studies in people. However, renal disease in humans and cats is different, because cats have predominantly tubular disease, whereas people more often have glomerular disease.

A European study evaluated benazepril in cats with chronic renal failure (CRF). There were 193 cats with CRF randomized to receive either placebo or benazepril (0.5-1 mg/kg q24h PO). Results showed:

• No difference in creatinine concentrations or progression of renal insufficiency between groups.
• Quality of life was improved in cats receiving benazepril, but the reason is unsure, as no differences were found in renal function between the 2 groups.
• Cats with renal failure and proteinuria (UP:CR > 1) which were treated with benazepril had enhanced survival and slowed progression of CRF.

Recommendations for use of ACE inhibitors in cats with CRF:

• Consider ACE inhibitors for cats with CRF, especially those with CRF and proteinuria. However, at high creatinine concentrations, administration of ACE inhibitors would be contraindicated. For example, in people with CRF, administration of ACE inhibitors commonly causes a 15-to-20% increase in creatinine concentration. Thus, one needs to become concerned about ACE inhibitors making azotemia worse at creatinine concentrations between 3 - 4 mg/dL. For cats with creatinine concentrations > 4 mg/dL, ACE inhibitors are used at a lower dose (0.5 mg/kg) and only if the cat is proteinuric. The animal should be monitored closely, and creatinine should be rechecked 5-7d after commencing treatment. It probably does not matter which ACE inhibitor is used (benazepril, enalapril, or other).

Thyroxine has both a trophic and functional effect on renal function. When cats are given T4 supplement, glomerular filtration rate (GFR) increases by as much as 50%, systemic blood pressure increases by ≡ 5 mmHg., and kidney size increases. These changes revert to normal by ~ 6 weeks after discontinuing T4 supplementation.