Beta-adrenergic antagonists

Beta-adrenergic antagonists

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

·                 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 distrib-uted 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 me-tabolized 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 ini-tially I.V., and then orally. Metoprolol may also be used for heart failure.

Because of their ability to reduce blood pressure, beta-adren-ergic 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 neg-ative addictive effects on SA or AV node conduction when admin-istered with a beta-adrenergic blocker.

·                 Diuretics or other hypotensive agents can potentiate the hy-potensive 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 al-tered by beta-adrenergic blockers.

·                 The ability of theophylline to produce bronchodilation is im-paired by nonselective beta-adrenergic blockers. (See Adverse re-actions to beta-adrenergic blockers.)