Amlodipine Besylate (Norvasc®, Istin®) for Dogs and Cats

Overview of Amlodipine Besylate for Canines and Felines

• Amlodipine Besylate, a high blood pressure medication, better known as Norvasc® or Istin®, is used for dogs and cats to treat high blood pressure and congestive heart failure. Amlodipine is also available other drugs such as Amlodipine with benazapril is called Lotrel® and Amlodipine with Atorvastatin is Caduet®. The article below refers to the use of Amlodipine as the only drug.
• High blood pressure (hypertension) is a serious medical problem in dogs and cats. It has not been recognized as frequently in pets as it has in people because routine blood pressure monitoring is not commonly performed.
• Effective treatment of hypertension reduces injury to the “target organs” – the brain, eyes, heart and kidneys. Left untreated, hypertension can lead to stroke, detached retinas and blindness, heart thickening and kidney failure.
• Blood pressure depends on the activity of the heart and the resistance offered by blood vessels. Blood vessels have high resistance when constricted, low resistance when relaxed (dilated).
• Blood vessel constriction is determined by the amount of calcium ions entering the blood vessel wall. Calcium causes the smooth muscle of the blood vessels to constrict.
• Amlodipine besylate is a drug classified as a dihydropyridine calcium channel blocker. This drug blocks calcium entry into muscle cells and causes the blood vessel to relax, lowering the blood pressure.
• Amlodipine is a prescription drug and can only be obtained from a veterinarian or by prescription from a veterinarian.
• This drug is not approved for use in animals by the Food and Drug Administration but it is prescribed legally by veterinarians as an extra-label drug.

Brand Names and Other Names of Amlodipine Besylate

• This drug is registered for use in humans only.
• Human formulations: Norvasc® (Pfizer)
• Veterinary formulations: None

Uses of Amlodipine for Dogs and Cats

• The main use of amlodipine is to treat high blood pressure in cats and dogs.
• It is also used as a vasodilator drug in the treatment of congestive heart failure in dogs. Amlodipine will lower the blood pressure, making it easier for the heart to pump.

Precautions and Side Effects

• While generally safe and effective when prescribed by a veterinarian, amlodipine can cause side effects in some dogs and cats.
• Amlodipine should not be used in animals with known hypersensitivity or allergy to the drug.
• Use of some medications should be avoided in animals that have hypertension. Pet owners should discuss all current medications that the pet is receiving when treating hypertension. Some drugs that may exacerbate high blood pressure are phenylpropanolamine (PPA) and asthma medications.
• Amlodipine may interact with other medications. Consult with your veterinarian to determine if other drugs your pet is receiving could interact with amlodipine. Such drugs include diuretics and other drugs to lower blood pressure.
• The most important side effect is low blood pressure or hypotension caused by excessive dilation of arteries. This results in depression, weakness or even fainting.
• Blood pressure should be monitored periodically in dogs and cats receiving this drug.
• Loss of appetite may be observed and is the most common side effect.
• Missed doses can cause rapid increases in blood pressure.
• Depression of heart muscle contraction can occur, but this is less likely with a calcium channel blocker of this class.

How Amlodipine Is Supplied

• Amlopidine is available in 2.5, 5 and 10 mg tablets. These need to be cut with a pill cutter for use in cats and dogs.

Dosing Information of Amlodipine Besylate for Dogs and Cats

• Medication should never be administered without first consulting your veterinarian.
• Cats: the dose of Amlodipine used is 1/4 of a 2.5 mg tablet once daily orally, to control blood pressure. Doses as high as 1/2 of a 2.5 mg tablet twice daily may be needed for effective control.
• Dogs: the dose of Amlodipine used is 0.1 to 0.2 mg per pound (0.2 to 0.4 mg/kg) once to twice daily. A dose of 0.05 to 0.1 mg per pound is often started then the dose is increased while monitoring blood pressure.
• The duration of administration depends on the condition being treated, response to the medication and the development of any adverse effects. Be certain to complete the prescription unless specifically directed by your veterinarian. Even if your dog or cat feels better, the entire treatment plan should be completed to prevent relapse or prevent the development of resistance.