Atenolol
Atenololum (ICI-66082)
Also known as: Tenormin · Atenololum · ICI-66082
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Cardiac arrhythmias, obstructive heart disease, hypertension, myocardial infarction, etc. | 0.3-0.6 mg/kg PO q12h | PO | q12h | — | 🌎 NA |
| Moderate to severe sub-valvular aortic stenosis (SAS) | 0.5-1 mg/kg PO twice a day | PO | q12h | — | 🌎 NA |
| To attempt to decrease syncopal episodes associated with pulmonic stenosis | 0.25-1 mg/kg PO twice a day | PO | q12h | — | 🌎 NA |
| Hypertension | 0.25-1 mg/kg PO q12h | PO | q12h | — | 🌎 NA |
- Cardiac arrhythmias, obstructive heart disease, hypertension, myocardial infarction, etc.: For refractory VTach combine with mexiletine (5-8 mg/kg PO q8h)
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Treatment of hypertension or cardiac conditions (e.g., hypertrophic cardiomyopathy) | 3 mg/kg PO q12h (or 6.25 -12.5 mg total dose) PO q12h | PO | q12h | — | 🌎 NA |
| Treatment of hypertension or cardiac conditions | 6.25-12.5 mg (total dose per cat) q12h | PO | q12h | — | 🌎 NA |
| Treatment of choice for hyperthyroid, hypertensive cats | 6.25-12.5 mg (total dose) PO q12-24h | PO | q12-24h | — | 🌎 NA |
- Treatment of choice for hyperthyroid, hypertensive cats: Beta-blockers are rarely sufficient alone to treat hypertension due to other causes.
Ferrets
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Hypertrophic cardiomyopathy | 6.25 mg (total dose) PO once daily | PO | q24h | — | 🌎 NA |
| Hypertrophic cardiomyopathy | 3.13-6.25 mg (total dose) PO once daily | PO | q24h | — | 🌎 NA |
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Atenolol is a cardioselective beta-blocker used primarily for the management of systemic hypertension and tachyarrhythmias in small animals. It is frequently utilized in cats with hypertrophic cardiomyopathy (HCM) without accompanying pulmonary edema to reduce dynamic outflow tract obstruction and improve diastolic filling.
Key Highlights:
- Cardioselective: Has minimal beta-2 activity at usual doses, making it comparatively safer to use in asthmatic or bronchospastic patients than non-selective beta-blockers like propranolol.
- Negative Inotrope: Must be used with extreme caution in patients with congestive heart failure (CHF), renal failure, or sinus node dysfunction.
- Metabolic Effects: Higher dosages may mask clinical signs of hyperthyroidism or hypoglycemia. It can also cause hyper- or hypoglycemia, requiring caution in brittle diabetics.
Clinical Pearl: Unlike propranolol, atenolol is highly hydrophilic. It has low lipid solubility, meaning it minimally crosses the blood-brain barrier, resulting in significantly fewer central nervous system (CNS) side effects (like lethargy or depression). Because it is primarily excreted unchanged by the kidneys, dosage adjustments may be necessary in patients with significant renal impairment.
Mechanism of action
Atenolol acts as a competitive, relatively specific antagonist at β1-adrenergic receptors located primarily in the myocardium.
- Pathway: Blockade of β1-receptors → decreased intracellular cAMP → reduced intracellular calcium influx.
- Cardiovascular Effects: This leads to negative chronotropic (decreased sinus heart rate) and negative inotropic (decreased contractility) effects. It slows AV conduction, diminishes cardiac output at rest and during exercise, and significantly decreases myocardial oxygen demand.
- Blood Pressure: Reduces systemic blood pressure through decreased cardiac output and potentially decreased renin release from the kidneys.
- Selectivity Loss: At higher dosages, β1 specificity may be lost, leading to β2-receptor blockade (which can cause bronchoconstriction and peripheral vasoconstriction).
- Atenolol lacks intrinsic sympathomimetic activity (ISA) and membrane-stabilizing activity.
Safety & warnings
Contraindications
- Overt heart failure
- Hypersensitivity to beta-blockers
- Greater than first-degree heart block
- Sinus bradycardia
- Cats with hypertrophic cardiomyopathy with accompanying pulmonary edema
Adverse effects
- Lethargy
- Hypotension
- Diarrhea
- Bradycardia
- Inappetence
- Depression
- Impaired AV conduction
- Worsening of heart failure
- Hypoglycemia
- Syncope
- Bronchoconstriction (rare at normal doses)
Precautions
Withdrawal Warning: Exacerbation of symptoms has been reported following abrupt cessation of beta-blockers. It is highly recommended to withdraw therapy gradually in patients who have been receiving the drug chronically.
- Renal Impairment: Use cautiously in patients with significant renal insufficiency as the drug is primarily excreted unchanged in the urine.
- Endocrine: Can mask clinical signs associated with hypoglycemia and thyrotoxicosis. Use cautiously in labile diabetic patients as it can cause hypo- or hyperglycemia.
- Cardiac: Use cautiously in patients with sinus node dysfunction. Non-specific beta-blockers are generally contraindicated in patients with CHF unless secondary to a tachyarrhythmia responsive to beta-blocker therapy.
Drug interactions
Additive myocardial depression may occur with concurrent use.
Concurrent use should be done with caution due to additive negative inotropic effects, particularly in patients with preexisting cardiomyopathy or CHF.
Atenolol may exacerbate rebound hypertension after stopping clonidine therapy.
May increase the hypotensive effects of atenolol.
Concurrent use may exhibit enhanced hypotensive effects.
Potential for additive effects including hypotension and bradycardia.
May have their actions blocked by atenolol, and they may in turn reduce the efficacy of atenolol.
Monitoring
- Cardiac function
- Pulse rate
- ECG (if necessary)
- Blood pressure (if indicated)
- Signs of toxicity (lethargy, hypotension, bradycardia)
Pharmacokinetics
Half-life
Absorption
Absorbed rapidly. Bioavailability is approximately 90% in cats, but only 50-60% in humans.
Distribution
Very low protein binding (5-15%) and distributed well into most tissues. Low lipid solubility; only small amounts distribute into the CNS. Crosses the placenta and levels in milk are higher than those found in plasma.
Metabolism
Minimally biotransformed in the liver.
Elimination
40-50% is excreted unchanged in the urine and the bulk of the remainder is excreted in the feces unchanged (unabsorbed drug). Duration of beta blockade effect in cats persists for about 12 hours.
Overdose
Common clinical signs of overdose include lethargy and vomiting. Severe overdose represents extensions of the drug's pharmacologic effects: hypotension, bradycardia, bronchospasm, cardiac failure, hypoglycemia, and hyperkalemia.
Treatment:
- If recent oral ingestion: consider emptying the gut and administering activated charcoal.
- Monitor: ECG, blood glucose, potassium, and blood pressure.
- Cardiovascular support: Symptomatic treatment. Use fluids and pressor agents (dopamine or norepinephrine) for hypotension.
- Bradycardia: Treat with atropine. If atropine fails, isoproterenol given cautiously is recommended.
- Metabolic: Insulin and dextrose may be needed for hyperkalemia and hypoglycemia.
- Advanced support: A transvenous pacemaker may be necessary. Cardiac failure can be treated with a digitalis glycoside, diuretics, and oxygen.
- Antidote: Glucagon (5-10 mg IV; human dose) may increase heart rate and blood pressure and reduce the cardiodepressant effects of atenolol.
Available products
Formulations
- Oral tablets
- Oral suspension (compounded)
Human-labeled
- Atenolol Oral Tablets: 25 mg, 50 mg, & 100 mg; Tenormin® (AstraZeneca); generic; (Rx)
- Also available in an oral fixed dose combination product with chlorthalidone.
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Tablets should be stored at room temperature and protected from heat, light, and moisture. Atenolol preparations are most stable at pH 4 and should be protected from ultraviolet light to prevent decomposition. Compounding Note: Atenolol oral suspensions should NOT be compounded with sugar-containing vehicles (like simple syrup), as sugars reduce potency to <90% within 7-14 days. Suspensions compounded with sugar-free vehicles (Ora-Plus/Ora-Sweet SF) retain >90% potency for 90 days at 5°C and 25°C.
Client information
- Consistency is Key: To be effective, your pet must receive all doses exactly as prescribed by your veterinarian.
- Do Not Stop Abruptly: Never stop this medication suddenly without consulting your veterinarian, as this can cause dangerous spikes in heart rate and blood pressure. If the medication needs to be stopped, it must be withdrawn gradually.
- Monitor for Side Effects: Notify your veterinarian immediately if your pet becomes unusually lethargic, shows exercise intolerance, develops shortness of breath or a cough, or exhibits a sudden change in behavior or attitude.
- Pill Splitting: Tablets may be crushed or split into quarters or halves for appropriate dosing as directed.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.