Factors Influencing the Relationship Between the Dose of Amlodipine Required for Blood Pressure Control and Change in Blood Pressure in Hypertensive Cats

Abstract

BackgroundHypertension is a common problem in elderly cats. In most cats, systolic blood pressure (SBP) of <160 mmHg is achieved in response to amlodipine besylate at either 0.625 or 1.25 mg q24h. The individual cat factors determining dose requirement dose have not been explored.AimsTo determine whether individual cat factors influence the dose of amlodipine required to achieve adequate blood pressure control and to determine whether factors other than the prescribed dose of drug alter the achieved plasma amlodipine concentrations.MethodsFifty‐nine hypertensive cats that required 0.625 mg (A) and 41 cats that required 1.25 mg (B) amlodipine to reach a target SBP of <160 mmHg were identified, and plasma amlodipine concentrations were determined. Comparisons were made between groups, and multivariable linear regression models were performed to investigate predictors of antihypertensive response.ResultsCats that required a greater dose of amlodipine had significantly higher SBP at diagnosis of hypertension (A: (median [25th, 75th percentile]) 182 [175,192] mmHg; B: 207 [194,217] mmHg, P < .001), but comparable blood pressure was achieved after treatment. Plasma amlodipine concentrations were directly related to the dose of amlodipine administered. At diagnosis, cats in group B had significantly lower plasma potassium concentration (A: 4.1 [3.8,4.5]; B: 3.8 [3.6,4.2] mEq/L, P < .01). Weight did not differ between groups. The decrease in SBP was directly and independently associated with the SBP at diagnosis and the plasma amlodipine concentration.Conclusions and Clinical ImportanceCats with higher blood pressure at diagnosis might require a greater dose of amlodipine to control their blood pressure adequately. Differences in amlodipine pharmacokinetics between cats do not seem to play a role in the antihypertensive response.

Survival after diagnosis of hypertension in cats attending primary care practice in the United Kingdom

“…Cats requiring an increase in amlodipine dose were found to have significantly higher blood pressure at diagnosis in comparison to those that did not. This finding is in agreement with a recent study, even though not all cats had a follow‐up blood pressure measurement to ensure adequate blood pressure control in our study. Because of inadequate monitoring, it was not possible to investigate the association between blood pressure control and survival after hypertension diagnosis.…”

“…Target organ damage is associated with considerable morbidity, including blindness, ventricular hypertrophy, proteinuria, and hypertensive encephalopathy . Amlodipine, a calcium channel blocker, is recommended for the treatment of hypertension and has been found to be effective at decreasing blood pressure in hypertensive cats …”

ACVIM consensus statement: Guidelines for the identification, evaluation, and management of systemic hypertension in dogs and cats

“…Despite the potential role of either the systemic or intrarenal RAAS axis in the pathogenesis or maintenance of hypertension, CCB, specifically amlodipine besylate, have been the first choice for antihypertensive treatment because of established efficacy in cats with idiopathic hypertension or in those with CKD. A mean decrease in SBP of 28‐55 mm Hg typically is observed in cats in hypertensive to severely hypertensive cats .…”

“…A mean decrease in SBP of 28‐55 mm Hg typically is observed in cats in hypertensive to severely hypertensive cats . Recent data indicate that an initial starting dose of 0.625 mg per cat per day amlodipine besylate is effective in cats in which initial SBP is <200 mm Hg, but that those cats with SBP >200 mm Hg may benefit from a higher starting dosage of 1.25 mg per cat per day . Rarely, dosages of up to 2.5 mg per cat per day however may be required.…”

Visual outcome in cats with hypertensive chorioretinopathy

“…There are a number of studies assessing the effect of blood pressure on cardiac and renal disease, and survival time of cats with systemic hypertension, but there is very little information available on the rate of retinal reattachment, return of vision, or long‐term visual outcome in cats with hypertensive chorioretinopathy . Thus, the goal of this study was to investigate the factors associated with long‐term visual outcome in cats with retinal disease attributable to systemic hypertension presenting to specialty ophthalmology practices.…”