Usage
Atenolol is primarily prescribed for:
- Hypertension (high blood pressure)
- Angina pectoris (chest pain)
- Cardiac dysrhythmias (irregular heartbeats)
- Myocardial infarction (heart attack) – both early intervention and long-term prophylaxis.
- Migraine prophylaxis
It is pharmacologically classified as a beta-blocker, specifically a beta-1 selective adrenergic receptor blocking agent. Atenolol works by selectively blocking beta-1 adrenergic receptors in the heart, reducing heart rate, myocardial contractility, and cardiac output, thus lowering blood pressure and reducing the workload on the heart.
Alternate Names
Atenolol is the generic name. Brand names include Tenormin, Atenolol Viatris.
How It Works
Pharmacodynamics: Atenolol primarily affects the cardiovascular system. It competitively blocks beta-1 adrenergic receptors located in the heart. This action leads to a decrease in heart rate, contractility, and cardiac output, ultimately lowering blood pressure and myocardial oxygen demand. Atenolol also inhibits renin release, further contributing to its antihypertensive effect. It has minimal effect on beta-2 receptors at usual therapeutic doses, making it cardioselective.
Pharmacokinetics:
- Absorption: Atenolol is absorbed incompletely (around 50%) after oral administration. Peak plasma concentrations are reached within 2-4 hours.
- Distribution: It is poorly lipid-soluble and distributes mainly in the extracellular fluid. It crosses the placental barrier and is present in breast milk.
- Metabolism: Atenolol undergoes minimal hepatic metabolism, with a large portion of the dose excreted unchanged.
- Elimination: Primarily excreted renally (through the kidneys), with a half-life of 6-7 hours in adults, but prolonged in neonates and individuals with renal impairment.
Mode of Action: Atenolol competitively binds to beta-1 adrenergic receptors in the heart, preventing the binding of catecholamines like norepinephrine and epinephrine. This inhibition reduces the activation of adenylate cyclase and the subsequent formation of cyclic AMP, which ultimately decreases heart rate, contractility, and cardiac output.
Elimination Pathways: Predominantly renal excretion of unchanged drug.
Dosage
Standard Dosage
Adults:
- Hypertension: Initial dose is 25-50 mg once daily, which can be increased to 100 mg once daily if needed.
- Angina: Initial dose is 50 mg once daily, which can be increased to 100 mg once daily or 50 mg twice daily. Some patients may require 200 mg daily.
- Arrhythmias: 50-100 mg once daily.
- Migraine Prophylaxis: 25-100 mg twice daily.
- Post-Myocardial Infarction: Initial dose is 5-10 mg IV followed by 50 mg oral about 15 minutes later. After 12 hours, administer 50 mg oral, and then 100 mg once daily for maintenance.
Children: Dosage must be determined by the doctor based on weight and age, generally 0.5–2 mg/kg daily, not to exceed 100mg/day.
Special Cases:
- Elderly Patients: Initial dose 25 mg once daily, titrated cautiously as needed due to potential age-related decline in renal function.
- Patients with Renal Impairment: Dose adjustment required based on creatinine clearance. For creatinine clearance 15-35 mL/min, 50 mg once daily; for creatinine clearance <15 mL/min, 25 mg daily or 50 mg on alternate days. For patients on hemodialysis: 25-50 mg after each session under close supervision due to the risk of significant blood pressure drops.
- Patients with Hepatic Dysfunction: Atenolol undergoes minimal hepatic metabolism, so dosage adjustments are generally not necessary.
- Patients with Comorbid Conditions: Caution should be exercised in patients with diabetes, chronic obstructive pulmonary disease (COPD), peripheral vascular disease, or myasthenia gravis. Dosage adjustment may be required.
Clinical Use Cases
- Intubation: Atenolol may be used to control heart rate and blood pressure during intubation, but dosage should be titrated cautiously based on patient response.
- Surgical Procedures: May be used in perioperative settings for blood pressure control. Dosage to be determined by the anesthesiologist.
- Mechanical Ventilation: Dosage adjustment may be needed to maintain hemodynamic stability.
- Intensive Care Unit (ICU) Use: Atenolol use in the ICU setting should be closely monitored with dosage adjustments based on patient’s hemodynamic status.
- Emergency Situations: Atenolol can be used in hypertensive emergencies, but other agents may be preferred.
Dosage Adjustments:
Dose modifications are required in patients with renal impairment, and potentially in the elderly. Consider metabolic disorders and genetic polymorphisms that impact drug metabolism when determining the appropriate dosage.
Side Effects
Common Side Effects:
Dizziness, lightheadedness, fatigue, drowsiness, depression, nausea, diarrhea, cold hands and feet, bradycardia, hypotension.
Rare but Serious Side Effects:
Bradycardia, heart failure exacerbation, bronchospasm, dyspnea, heart block.
Long-Term Effects:
Fatigue, sexual dysfunction, depression, and potentially worsening of peripheral vascular disease.
Adverse Drug Reactions (ADR):
Severe bradycardia, hypotension, heart failure, bronchospasm. These require immediate intervention.
Contraindications
- Second or third-degree heart block (without a pacemaker)
- Cardiogenic shock
- Severe bradycardia
- Sick sinus syndrome
- Severe, uncontrolled heart failure
- Hypersensitivity to atenolol.
Drug Interactions
Atenolol interacts with numerous medications, including:
- Calcium channel blockers (verapamil, diltiazem): Can cause additive bradycardia and hypotension.
- Clonidine: Avoid abrupt discontinuation of clonidine while taking atenolol as it can cause rebound hypertension.
- Digoxin: Can increase the risk of bradycardia.
- Insulin and oral hypoglycemics: May mask the symptoms of hypoglycemia.
- Other beta-blockers: Additive effects.
- CYP450 interactions: Minimal due to limited hepatic metabolism.
- Alcohol: may intensify atenolol side effects such as dizziness.
Pregnancy and Breastfeeding
- Pregnancy Safety Category: Category D. Atenolol crosses the placental barrier. Use only if potential benefit justifies the risk to the fetus. Can cause fetal bradycardia, hypotension, and growth restriction.
- Breastfeeding: Atenolol is excreted in breast milk and can cause neonatal bradycardia, hypotension, and hypoglycemia. Monitor infants for signs of beta-blockade. Other beta-blockers might be preferred.
Drug Profile Summary
- Mechanism of Action: Beta-1 selective adrenergic receptor blocker, reducing heart rate, contractility, and cardiac output.
- Side Effects: Dizziness, fatigue, bradycardia, hypotension. Serious: heart failure, bronchospasm, heart block.
- Contraindications: Heart block, cardiogenic shock, severe bradycardia, uncontrolled heart failure, hypersensitivity.
- Drug Interactions: Calcium channel blockers, clonidine, digoxin, insulin.
- Pregnancy & Breastfeeding: Category D; Use with caution during breastfeeding; monitor infant for bradycardia.
- Dosage: Adults: Hypertension: 25-100 mg/day; Angina: 50-200 mg/day. Pediatric: 0.5-2 mg/kg/day. Adjust dose based on patient’s renal function.
- Monitoring Parameters: Heart rate, blood pressure, electrocardiogram (ECG).
Popular Combinations
Atenolol is often combined with other antihypertensive agents like thiazide diuretics (e.g., chlorthalidone) for synergistic effects in lowering blood pressure.
Precautions
- General Precautions: Screen for allergies, renal/hepatic dysfunction, diabetes, COPD, and peripheral vascular disease.
- Specific Populations: Monitor pregnant women, breastfeeding mothers, children, and elderly patients closely.
- Lifestyle Considerations: Limit alcohol intake, as it can exacerbate some side effects.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Atenolol?
A: Adults: Hypertension/Angina: Initial 25-50 mg once daily, up to 100 mg/day. Post-MI: Initial 5-10 mg IV, followed by oral regimen. Children: 0.5-2 mg/kg/day, not exceeding 100mg/day. Adjust dosage based on renal function and individual response.
Q2: What are the most common side effects of Atenolol?
A: Dizziness, fatigue, bradycardia, and cold extremities are common side effects.
Q3: Can Atenolol be used during pregnancy?
A: Atenolol is a Pregnancy Category D drug. Use only if the potential benefits outweigh the risks to the fetus. It can cause fetal bradycardia, hypotension, and growth retardation.
Q4: How does Atenolol interact with calcium channel blockers?
A: Atenolol can interact with calcium channel blockers like verapamil and diltiazem, potentially causing additive bradycardia and hypotension. Monitor closely for these effects.
Q5: What should be done if a patient experiences bradycardia while on Atenolol?
A: If a patient develops significant bradycardia, discontinue atenolol and consider administering atropine or other appropriate interventions.
Q6: Is Atenolol safe for patients with asthma?
A: Atenolol, although cardioselective, can potentially exacerbate bronchospasm, especially at higher doses. Use with extreme caution in patients with asthma or COPD.
Q7: How should Atenolol be discontinued?
A: Atenolol should be tapered gradually under medical supervision to avoid rebound hypertension or other adverse events. Abrupt discontinuation is not advised.
Q8: Can atenolol be used in patients with renal impairment?
A: Yes, but dosage adjustments are necessary based on creatinine clearance.
Q9: What is the mechanism of action of Atenolol?
A: Atenolol selectively blocks beta-1 adrenergic receptors in the heart, leading to decreased heart rate, contractility, and cardiac output.
Q10: What are the contraindications for Atenolol?
A: Second or third-degree heart block (without a pacemaker), cardiogenic shock, severe bradycardia, severe uncontrolled heart failure, and hypersensitivity to atenolol are contraindications.
