Beta-adrenergic antagonists

Beta-adrenergic antagonists

Beta-adrenergic antagonists (also called beta blockers) are used for long-term prevention of angina and are one of the main types of drugs used to treat hypertension. Beta-adrenergic blockers include:

• atenolol
• metoprolol
• nadolol
• propranolol.

Pharmacokinetics

Metoprolol and propranolol are absorbed almost entirely from the GI tract, whereas less than one-half the dose of atenolol or nadolol is absorbed. These beta-adrenergic blockers are distributed widely. Propranolol is highly protein-bound; the other beta-adrenergic blockers are poorly protein-bound.

Making an escape

Propranolol and metoprolol are metabolized in the liver, and their metabolites are excreted in urine. Atenolol and nadolol aren’t metabolized and are excreted unchanged in urine and stool.

 

Pharmacodynamics

Beta-adrenergic blockers decrease blood pressure and block beta-adrenergic receptor sites in the heart muscle and the conduction system. This decreases the heart rate and reduces the force of the heart’s contractions, resulting in a lower demand for oxygen.

 

Pharmacotherapeutics

Beta-adrenergic blockers are indicated for long-term prevention of angina. In acute coronary syndrome, metoprolol may be given initially I.V., and then orally. Metoprolol may also be used for heart failure.

 

Because of their ability to reduce blood pressure, beta-adrenergic blockers are also first-line therapy for treating hypertension.

 

Drug interactions

A number of drugs interact with beta-adrenergic blockers.

• Antacids reduce absorption of beta-adrenergic blockers.
• Nonsteroidal anti-inflammatory drugs (NSAIDs) can decrease the hypotensive effects of beta-adrenergic blockers
• Cardiac glycosides and calcium channel blockers can have negative addictive effects on SA or AV node conduction when administered with a beta-adrenergic blocker.
• Diuretics or other hypotensive agents can potentiate the hypotensive effects of beta-adrenergic blockers.
• Lidocaine toxicity may occur when lidocaine is taken with beta-adrenergic blockers.
• The requirements for insulin and oral antidiabetics can be altered by beta-adrenergic blockers.
• The ability of theophylline to produce bronchodilation is impaired by nonselective beta-adrenergic blockers. 

Warning!

Adverse reactions to beta-adrenergic blockers

Beta-adrenergic blockers may cause:

• bradycardia
• angina
• fluid retention
• peripheral edema
• heart failure
• arrhythmias, especially atrioventricular block
• hypotension
• dizziness
• nausea and vomiting
• diarrhea
• significant constriction of the bronchioles.

Quick stop causes concern

Suddenly stopping a beta-adrenergic blocker may trigger:

• angina
• hypertension
• arrhythmias
• acute myocardial infarction.