Angiotensin-converting enzyme (ACE) inhibitors are receiving much attention for their role in managing cats with chronic renal
insufficiency. Benazepril (0.5 to 1.0 mg/kg orally every 24 hours) improves survival time, quality of life, appetite, and weight gain in proteinuric patients with chronic renal
insufficiency.13 Consider benazepril for patients with a urine protein-creatinine ratio of more than 0.4.
Anemia occurs in some patients with chronic renal insufficiency for a variety of reasons, including reduced erythropoietin
secretion, blood loss from uremic gastritis, and inadequate dietary protein that leads to reduced hemoglobin production. Consider treating patients with recombinant human erythropoietin when a nonregenerative anemia (packed cell volume [PCV] <20%)
is present. Administer 75 to 100 U/kg of erythropoietin subcutaneously three times a week until the PCV returns to low normal
(24% to 30%). Then reduce the dose and frequency to 50 to 75 U/kg subcutaneously two times a week. Monitor the PCV and blood
pressure carefully, especially in the first 60 to 90 days of treatment, because anti-erythropoietin antibodies can form in
up to 20% of treated cats, leading to severe anemia. If the PCV declines severely during treatment, stop administering the drug and, if necessary, provide blood transfusions until the patient's PCV recovers and stabilizes.
Hyperthyroidism and chronic renal insufficiency
Hyperthyroidism and chronic renal insufficiency are common diseases of senior cats and often occur concurrently. Diagnosis can be difficult because the clinical signs of the two illnesses can overlap.
About 50% of cats with both hyperthyroidism and chronic renal insufficiency will have a normal total T4 concentration on a single measurement.13 If a cat with chronic renal insufficiency has a palpable thyroid nodule and a normal
T4 concentration, pursue a diagnosis of hyperthyroidism using thyroid scintigraphy or T3-suppression testing.
Hyperthyroidism causes increased glomerular filtration rate and renal blood flow, which may mask underlying chronic renal
insufficiency. Many cats with both diseases will be azotemic at the time of diagnosis. However, azotemia develops following
hyperthyroidism treatment in about 15% to 23% of cats.13 When you treat hyperthyroidism, renal blood flow and glomerular filtration
rates decrease, revealing chronic renal insufficiency in cats that had marginal renal function before therapy.
Managing cats with concurrent hyperthyroidism and chronic renal insufficiency presents special challenges. If a cat has hyperthyroidism
and azotemia or you suspect chronic renal insufficiency, perform a methimazole challenge test. This allows a reversible way
to treat the hyperthyroidism while evaluating renal function. Start methimazole treatment at 2.5 mg/cat every 12 hours and
re-evaluate a serum chemistry profile for renal function and T4 levels after two weeks if you administer the drug orally and after four weeks if you administer the drug transdermally. If renal
function is stable, you may increase the methimazole dose to achieve euthyroidism.
If the cat retains stable renal function once euthyroidism is achieved with methimazole, you may institute long-term therapy
or pursue radioiodine treatment or thyroidectomy. If renal function deteriorates, you and the owner must make treatment choices. You may opt to
continue treatment with methimazole to control hyperthyroidism and manage any clinical signs of chronic renal insufficiency
that develop. These patients often fare best when you adjust their methimazole dosages to achieve a total T4 concentration in the upper end of the reference range. Or you may opt to treat the hyperthyroidism with atenolol (6.25 to
12.5 mg/cat orally every 24 hours) instead to reduce the cardiovascular effects of the disease and delay azotemia onset by avoiding the use of methimazole. With careful monitoring and management, these cats can have a good quality of life and be rewarding to treat.
Hypertension is the most important cardiovascular disease affecting geriatric cats because of its devastating impact on many
body systems, including the eyes, kidneys, heart, and central nervous system. Many cases of feline hypertension are secondary
to an underlying disease. For example, hypertension occurs in 29% or more of patients with chronic renal insufficiency, but
17% to 50% of cases may represent essential or primary hypertension.14 I recommend performing blood pressure screening for all geriatric cats as well as cats with such conditions as chronic renal
insufficiency, hyperthyroidism, and heart disease.