What is the Difference Between Atenolol and Metoprolol

The key difference between Atenolol and Metoprolol is that Atenolol is water soluble and cannot easily cross the blood-brain barrier, while Metoprolol is lipid soluble and readily cross the blood-brain barrier and more likely to produce sleep disturbances and nightmares.

Atenolol and Metoprolol are beta-blockers that block the effects of adrenalin and other hormones in the heart and blood vessels. This helps to lower blood pressure, slow the heart rate, and reduce the workload on the heart. Both these two drugs are FDA-approved to treat hypertension, angina, and heart failure. Atenolol and Metoprolol are very similar in their mode of action and side effects. However, some differences between the two drugs can be observed in their pharmacological properties.

CONTENTS

1. Overview and Key Difference
2. What is Atenolol 
3. What is Metoprolol
4. Similarities – Atenolol and Metoprolol
5. Atenolol vs Metoprolol in Tabular Form
6. Summary – Atenolol vs Metoprolol

What is Atenolol?

Atenolol is a cardio-selective beta-blocker prescribed to manage hypertension and chronic angina and to reduce the mortality associated with myocardial infarction in hemodynamically stable patients. In addition, the off-label effects of Atenolol include secondary prevention of myocardial infarction and management of heart failure and atrial fibrosis. Atenolol is a synthetic small molecule chemically known as C₁₄H₂₂N₂O₃ with a molecular weight of 266.3361 g/mol. Although Atenolol is one of the most prescribed beta-blockers, some studies suggest that Atenolol may only moderately reduce the risk of cardiovascular conditions in patients with hypertension.

Atenolol is a selective antagonist of the β1-adrenergic receptor, and it exerts most of its effects on the heart by preventing the increase of heart rate, electrical conductivity, and contractility. Upon oral administration, approximately 50% of Atenolol is absorbed in the gastrointestinal tract. A small amount of Atenolol binds with serum albumin and crosses the blood-brain barrier slowly. The drug is then minimally metabolized in the liver and excreted in the urine. However, 85% of IV-administered drugs are eliminated with urine, while 10% are excreted with feces, with an elimination half-life of 6-7 hours. No adverse effects on fertility have been found in male and female mice, while the drug has appeared in breast milk, suggesting the possible side effects in infants.

What is Metoprolol?

Metoprolol is another beta-blocker used to manage hypertension and chronic angina and reduce the mortality associated with myocardial infarction. Metaprolol is also a small molecule primarily designed as immediate-release and extended-release formulations. The chemical formula of Metoprolol is C₁₅H₂₅NO_3, with an average molecular weight of 267.3639 g/mol. The drug was initially developed in 1969 and received FDA approval in 1978. The effect of Metoprolol is primarily related to the beta-1-adrenergic receptor and is specific to cardiac cells. The inhibition of the beta-1-adrenergic receptor decreases the cardiac output by producing a negative chronotopic and ionotropic effect.

Oral administration of Metropolol results in complete absorption in the gastrointestinal tract with a maximum serum concentration of 1-2 hours. In addition, intravenous administration of Metoprolol is associated with 100% bioavailability. The drug is not extensively bound with plasma proteins and undergoes a significant first-pass effect in the liver. Urine mainly excretes Metropolol with a half-life of 3-7 hours. It has not been associated with carcinogenesis or impaired fertility. However, Metoprolol treatment has been associated with increased macrophages in alveoli and slight biliary hyperplasia.

What are the Similarities Between Atenolol and Metoprolol?

• Atenolol and Metoprolol are used to treat hypertension, angina, heart failure, heart attack, arrhythmias, migraine headaches, and thyroid problems.
• They are generally considered safe and effective medications.
• Both drugs have side effects, such as slow heart rate, low blood pressure, fatigue, dizziness, headache, breathing problems, sleep problems, and nightmares.
• They are both available as generic drugs.

What is the Difference Between Atenolol and Metoprolol?

Atenolol and Metoprolol are commonly prescribed beta-blockers to slow the heart rate and lower the blood pressure. Both these medications work by blocking the effect of adrenalin and noradrenalin on the heart and blood vessels. However, several important differences can be observed between these two drugs. The key difference between Atenolol and Metoprolol is that Atenolol is water soluble and cannot cross the blood-brain barrier, while Metoprolol is soluble in lipids and can cross the blood-brain barrier.

Atenolol has an elimination half-life of 6-7 hours and is prescribed as a once-daily dose. In contrast, Metoprolol has an elimination half-life of 3-4 hours and is prescribed as a twice-daily dose. No food effect is associated with Atenolol, while the levels of Metoprolol are enhanced by food. There is enough evidence to prove the positive risk for pregnant individuals and categorized as a category D drug. Nevertheless, the effect of Metoprolol on pregnant individuals is unclear; it is still categorized as a category C drug since the risk cannot be ruled out.

Below is a summary of the difference between Atenolol and Metoprolol in tabular form for side-by-side comparison.

Summary – Atenolol vs. Metoprolol

Atenolol and Metoprolol are beta-blockers that block the effect of adrenalin and noradrenalin on the heart and blood vessels. These medications are commonly prescribed to treat high blood pressure, angina, and heart failure. However, there is a distinct difference between Atenolol and Metoprolol. Atenolol is water-soluble and cannot cross the blood-brain barrier, while Metoprolol is lipid-soluble and can cross the blood-brain barrier. This means Metoprolol is more likely to cause side effects such as sleep disturbances and nightmares. Atenolol also has a longer half-life (6-7 hours) than Metoprolol (3-4 hours), so it needs to be taken less often. Ultimately, the best beta-blocker for individual cases will depend on their needs and circumstances.

Reference:

1. Carlberg, Bo, et al. “Atenolol in hypertension: Is it a wise choice?” The Lancet, vol. 364, no. 9446, 2004, pp. 1684–1689.
2. Prakash, Amitabh, and Anthony Markham. “Metoprolol.” Drugs, vol. 60, no. 3, 2000, pp. 647–678.

Image Courtesy:

1. “Atenolol structure” By Ed (Edgar181) – Own work (Public Domain) via Commons Wikimedia
2. “Metoprolol structure” By Yikrazuul – Own work (Public Domain) via Commons Wikimedia