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Feline Hypertension: Clinical Findings and Response To Antihypertensive Treatment in 30 Cases
Sm Anim Clin Endocrinol 12[2]:5 May-Aug'02 Clinical Study 0 Refs

C.B. Chastain, DVM, MS, Dipl. ACVIM & Dave Panciera, DVM, MS, Dipl. ACVIM
Elliott J, Barber PJ, Syme HM, et al. J Sm Anim Pract 2001;42:122-129

BACKGROUND: Hyperthyroidism can cause high-output systolic hypertension from its inotropic effects. Chronic hypertension can cause nephrosclerosis and exacerbation of hypertension or chronic renal insufficiency may be separate from, but concurrent with, hyperthyroidism. Other potential effects of chronic hypertension include damage to the eye, brain, and heart. The frequency and severity of hypertension and renal insufficiency in hyperthyroid cats is not known.

SUMMARY: Thirty cats with signs of hyperthyroidism or kidney disease were found to have systolic blood pressure measurements in excess of 175 mmHg twice at least one week apart or one measurement in excess of 175 mmHg associated with acute blindness. Blood and urine samples were collected prior to treatment with amlodipine besylate, 0.625 mg per day, for routine hemogram, serum chemistries, and urinalysis and every six to 12 weeks thereafter for a minimum of three months. Ten cases were treated with additional drugs to control blood pressure, including benazepril, propranolol, atenolol, enalapril, and hydrochlorthiazide. Cats with clinical signs of hyperthyroidism, palpable nodules in the ventral cervical area, or elevated activity of alanine aminotransferase also were evaluated for plasma T4 concentration. Of the 30 hypertensive cats, four had hyperthyroidism under treatment and azotemia, one had untreated hyperthyroidism and azotemia, and two had untreated hyperthyroidism without azotemia. All but one of the 30 cats were 12 or more years of age. Thirty percent of the cats were presented for blindness and 60% had hypertensive retinopathy. Most cases of hypertension responded well to amlodipine with a lowered systolic blood pressure (mean of 153 from 202 mmHg) within 50 days. Systolic blood pressure did not exceed 165 mmHg in more than half of the cats for at least three months. The authors concluded that amlodipine is an effective long-term treatment for feline systemic hypertension.

CLINCIAL IMPACT: Renal insufficiency is the most common cause of systemic hypertension in the cat. Among 30 cats with systemic hypertension, seven had hyperthyroidism. Unless hyperthyroidism is accompanied by renal insufficiency, the degree of hypertension associated with hyperthyroidism alone is mild. Amlodipine is a calcium channel blocker with anti-hypertensive effects due to, its ability to produce peripheral arteriole dilation. Hypertension from hyperthyroidism is caused by high output, not arteriole constriction. The need to use antihypertensive treatment in addition to controlling hyperthyroidism in hyperthyroid cats is not clear, especially if renal insufficiency is not concurrent. Beta-blockers are preferable calcium-channel blockers for controlling hypertension resulting from an increased inotropic-effect and for tachyarrhythmia caused by hyperthyroidism. Amlodipine and beta blockers may be preferable in hyperthyroid cats with renal insufficiency and hypertension.

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