Amlodipine

Overview

Amlodipine (Norvasc®, Amodip®) is a dihydropyridine calcium-channel blocker widely used in veterinary medicine for the management of systemic arterial hypertension in dogs and cats. It is considered the first-line antihypertensive drug in small animals due to its potent and relatively selective vasodilatory effects.

In dogs and cats, hypertension is most commonly secondary to underlying diseases such as chronic kidney disease, hyperthyroidism, or endocrine disorders. Amlodipine is effective in lowering systemic blood pressure and reducing the risk of target organ damage involving the eyes, brain, heart, and kidneys.

Mechanism of Action (MOA): Amlodipine blocks L-type calcium channels primarily in vascular smooth muscle, resulting in peripheral arteriolar vasodilation and a reduction in systemic vascular resistance and afterload. Its effects on cardiac conduction and contractility are mild compared with non-dihydropyridine calcium-channel blockers, making it suitable for long-term use in dogs and cats with hypertension.

Indications

Amlodipine is used orally in dogs and cats for the management of systemic arterial hypertension and is widely considered the drug of choice for this indication in small animals. Treatment is aimed at reducing the risk of hypertension-associated target organ damage and improving clinical outcomes.

• Systemic hypertension (dogs and cats): Primary indication for amlodipine therapy, particularly in patients with persistent elevations in systolic blood pressure requiring pharmacologic control.
• Hypertension secondary to underlying disease: Commonly used in dogs and cats with hypertension associated with chronic kidney disease, hyperthyroidism (cats), or endocrine disorders, as part of a comprehensive disease management plan.
• Target organ damage due to hypertension: Used to reduce ongoing injury to organs such as the eyes (retinopathy, retinal detachment), brain (neurologic signs), heart (cardiac remodeling), and kidneys.
• Hypertensive emergencies (dogs and cats): May be used at higher monitored doses to rapidly reduce dangerously elevated blood pressure and limit acute organ damage.

In dogs, amlodipine is often added after initiation of a renin–angiotensin–aldosterone system (RAAS) inhibitor, whereas in cats it is commonly used as initial monotherapy. Blood pressure should be monitored regularly to guide dose adjustments and assess response.

Dosage (Reference)

Dog

In dogs, amlodipine is used for the management of systemic arterial hypertension. Therapy is usually initiated at the low end of the dose range and adjusted gradually based on blood pressure response and tolerance.

Cat

In cats, amlodipine is considered first-line therapy for systemic hypertension and is frequently used as monotherapy. Fixed per-cat dosing is commonly preferred.

Warnings & Precautions

Amlodipine is a potent peripheral vasodilator. While generally well tolerated in dogs and cats, careful patient selection, dose titration, and monitoring are essential to minimize adverse cardiovascular effects.

• Hypotension: Excessive blood pressure reduction may occur, especially during initiation of therapy or dose escalation. Use caution in animals at risk for hypotension and monitor systolic blood pressure closely.
• Cardiac disease: Use cautiously in dogs and cats with heart disease, particularly those with reduced cardiac output or severe aortic stenosis, as peripheral vasodilation may worsen hemodynamic compromise.
• Hepatic dysfunction: Amlodipine is extensively metabolized by the liver. Use lower initial doses and titrate slowly in patients with hepatic disease.
• Renal disease: Hypertension is often secondary to chronic kidney disease. When amlodipine is used alone, increased intraglomerular pressure may occur; combination therapy with an ACE inhibitor is commonly employed in dogs.
• Hypertensive emergencies: Close monitoring is required during the first 24–72 hours of therapy, especially in cats with severe hypertension or target organ damage.
• Proteinuria: In cats, amlodipine monotherapy may reduce proteinuria; however, concurrent renal disease should be monitored regularly.
• Shock and severe hypotension: Contraindicated in animals with shock or documented hypotension.
• Pregnancy and lactation: Safety has not been established in dogs or cats; use only if the potential benefits outweigh the risks.
• Pulmonary hypertension: Not recommended in dogs, as systemic hypotension may occur without meaningful improvement in pulmonary arterial pressures.

Drug Interactions

Clinically significant drug interactions with amlodipine are primarily related to additive hypotensive effects or alterations in drug metabolism. Careful dose adjustment and monitoring are recommended when amlodipine is used concurrently with the following medications in dogs and cats.

• Beta-adrenergic blockers (e.g., atenolol, propranolol): Additive reductions in blood pressure, heart rate, and myocardial contractility may occur, particularly in patients with underlying cardiac dysfunction.
• Other calcium-channel blockers (e.g., diltiazem): Concurrent use may enhance hypotensive and negative inotropic effects; use cautiously with close cardiovascular monitoring.
• ACE inhibitors and angiotensin receptor blockers (e.g., benazepril, telmisartan): Commonly used in combination for management of hypertension, but may produce additive blood pressure–lowering effects; blood pressure should be monitored closely.
• Cyclosporine: Amlodipine may increase cyclosporine blood concentrations; monitor for signs of cyclosporine toxicity and adjust dose if needed.
• Tacrolimus: Concurrent use may increase tacrolimus concentrations; enhanced monitoring is recommended.
• Strong CYP3A4 inhibitors (e.g., ketoconazole, itraconazole): May increase amlodipine plasma concentrations, increasing the risk of hypotension.
• CYP3A4 inducers (e.g., rifampin): May decrease amlodipine plasma concentrations and reduce antihypertensive efficacy.
• Clopidogrel: Amlodipine may reduce the antithrombotic effect of clopidogrel; clinical significance in dogs and cats is not fully established.
• Other hypotensive agents: Additive hypotensive effects may occur when combined with diuretics or other antihypertensive drugs.

Side Effects & Overdose

Side Effects

Amlodipine is generally well tolerated in dogs and cats. Adverse effects are usually mild, dose-dependent, and more likely to occur early in therapy or with excessive blood pressure reduction.

• Hypotension: Excessive lowering of systemic blood pressure may occur, particularly during dose initiation or escalation.
• Lethargy and weakness: May be observed secondary to reduced blood pressure.
• Inappetence: Decreased appetite has been reported in both dogs and cats, especially early in treatment.
• Gastrointestinal signs: Vomiting or diarrhea may occur but are generally uncommon.
• Reflex tachycardia: Occurs infrequently and is usually mild.
• Gingival hyperplasia: Reported as a long-term adverse effect in dogs and occurs rarely in cats; typically reversible after dose reduction or discontinuation.
• Peripheral edema: Uncommonly reported in dogs and may or may not resolve with discontinuation of therapy.
• Electrolyte abnormalities: Rare cases of azotemia or changes in potassium concentrations have been reported, particularly in patients with underlying renal disease.

Overdose

Overdose with amlodipine can result in severe cardiovascular effects due to excessive peripheral vasodilation. Clinical signs may be delayed and prolonged because of the drug’s long half-life.

• Severe hypotension: The most significant and potentially life-threatening effect.
• Tachycardia or bradycardia: May occur secondary to hypotension or direct cardiac effects.
• Lethargy and depression: Ranging from mild sedation to collapse.
• Gastrointestinal signs: Vomiting may occur, particularly following oral overdose.
• Respiratory distress: Rare but may occur secondary to cardiovascular compromise or pulmonary edema.
• Management: Treatment is supportive and may include intravenous fluids, calcium supplementation, vasopressors, and close cardiovascular monitoring.
• Advanced therapies: In severe cases, high-dose insulin euglycemic therapy, lipid emulsion therapy, or temporary pacing may be required.

Key Notes

Practical clinical pearls to optimize the safe and effective use of amlodipine in dogs and cats with systemic hypertension.

• Drug of choice: Amlodipine is considered the first-line antihypertensive medication in cats and a key component of therapy in dogs with systemic hypertension.
• Once-daily dosing: The long duration of action allows convenient once-daily administration, improving owner compliance.
• Gradual response: Blood pressure reduction is progressive rather than immediate; dose adjustments should be based on serial measurements, not single readings.
• Combination therapy: Often combined with RAAS inhibitors (e.g., ACE inhibitors or angiotensin receptor blockers) in dogs and cats with concurrent kidney disease or proteinuria.
• Vision recovery: Antihypertensive therapy may partially restore vision in some animals with hypertension-induced retinal damage, but response is variable.
• Individual dose variability: Effective doses vary widely between patients; dosing should be individualized based on blood pressure response.
• Long-term management: Most patients require lifelong therapy with regular reassessment and dose adjustment.
• Owner education: Emphasize the importance of consistent dosing and routine blood pressure monitoring to prevent target organ damage.