Overview
Therapeutic class:
Dihydropyridine calcium channel blocker
Species:
Cats and Dogs
Commonly prescribed by vets to treat:
Feline hypertension, reduce cardiac overload in dogs with mitral endocardiosis
Professional Monograph
Mode of Action
Amlodipine blocks calcium influx into vascular smooth muscle and to a lesser extent, cardiac
muscle. This results in vasodilation of systemic vascular resistance vessels and coronary arteries.
No negative inotropic effects.
Cats
Amlodipine is the drug of choice to treat feline hypertension. Studies revealed that amlodipine significantly
reduces systolic blood pressure in cats to less than 170mmHg within 7 days.
Hypertension in cats is normally secondary to other diseases eg renal failure, hyperthyroidism,
perirenal pseudocysts, glomerulonephropathy, adrenocortical disease, diabetes mellitus, etc. It is
often seen in middle aged to geriatric cats.
The four target organs of hypertension are the eye, central nervous system, kidney and the heart.
Cats can be presented with acute clinical signs secondary to hypertension eg blindness, seizures,
paresis and collapse.
Normal systolic pressure in a cat is <140mmHg. A cat is considered hypertensive if systolic blood
pressure is >160mmHg.
Most cats can be treated as outpatients, returning fortnightly to have their bloods pressure
checked until it is stabilised adequately. It is common for blood pressure to increase over time,
hence, 1 to 3 monthly blood pressure monitoring is recommended in treated cats.
Dogs
Systolic blood pressure of more than 160mmHg is considered hypertensive in a dog. In dogs,
diseases commonly associated with hypertension are renal disease, hyperadrenocorticism (Cushing’s
disease) and pheochromocytoma (catecholamine producing tumour of the adrenal medulla).
Amlodipine seems to be less effective to treat canine hypertension, even in high doses. ACE inhibitors
are frequently used first and amlodipine added later to treat persistent hypertension.
Amlodipine has been used as an adjunctive therapy for refractory heart failure caused by mitral
endocardiosis as an afterload reducer after ACE inhibitors maintenance therapy has been established.
Side Effects
Side effects of hypotension and inappetance is almost absent in cats. Azotaemia, lethargy, hypokalaemia,
reflex tachycardia and weight loss are rare but have been reported.
Precautions
Amlodipine is metabolized in the liver and dosage should be reduced if there is hepatic dysfunction.
Amlodipine has a slight negative inotrope effect. Hence, it should be used with caution in animals
with heart failure.
There have been recent concerns about the potential long term renal effects of amlodipine in cats
with chronic renal insufficiency. Amlodipine preferentially dilate the afferent glomerular arteriole. If
systemic blood pressure is reduced substantially, then glomerular hypertension will also be reduced.
The overall effect will be renal protective.
However, if the cat remains systemically hypertensive, then glomerular hypertension may persist
and be made worse with treatment with amlodipine. This may exacerbate renal injury. It is postulated
that using amlodipine together with an ACE inhibitor will help prevent this from happening.
Again, regular blood pressure monitoring is needed to ensure that blood pressure is maintained
<160mmHg.
Drug interactions
Concomitant use of amlodipine with diuretics, beta blockers, other vasodilators may cause hypotension.
Overdose
In cats, clinical signs of overdosage are lethargy and polydipsia. In dogs, clinical signs of overdosage
are anorexia, lethargy, tachycardia and bradycardia. Large overdoses should be treated with
gut emptying and supportive treatment.
CLIENT COUNSELLING INFORMATION
