Beta-blockers, also known as beta-adrenoceptor antagonists, are medications used to treat high blood pressure, angina and irregular heart beat. They are also used in eye drops to treat glaucoma. Beta-blockers act by tamping down the adrenergic nervous system, which is responsible for the "fight-or-flight" or adrenalin-driven bodily functions. When beta blockers suppress this function, they reduce blood pressure and heart rate.
Cardioselective Beta-Blockers
Beta-blockers can be classified as nonselective and beta-1 selective. Beta-1 selective drugs mainly affect the beta receptors responsible for heart rate and blood pressure control. They still affect beta receptors throughout the body, but to a lesser extent. Their action throughout the body is relative to the dose given. Drugs that mainly affect beta-1 receptors at lower doses will affect all types of beta receptors at higher doses.
Beta-blockers that are selective for beta-1 receptors tend to have fewer side effects. Beta-1 selective beta-blockers are also called cardioselective beta-blockers. Beta-blockers in this group are acebutolol (Sectral), atenolol (Tenormin), bisoprolol (Zebeta), esmolol (Brevibloc) and metoprolol (Lopressor).
Nonselective Beta-Blockers
Nonselective beta-blockers can also be used to prevent migraine headaches and tremors. Another drug in this group, propranolol, is sometimes used off-label to prevent performance anxiety or stage fright. Nonselective beta blockers include nadolol (Corgard), penbutolol (Levatol), pindolol (Visken), propranolol (Inderal) and sotalol (Betapace) and the eye drops cartelol (Ocupress) and timolol (Timoptic).
Third Generation Beta-Blockers
Third generation beta-blockers include both nonselective and cardioselective beta-blockers. These drugs tend to have additional activity as vasodilators, which helps them lower blood pressure further. Nonselective third generation beta-blockers are carvedilol (Coreg) and labetalol (Trandate). Cardioselective third generation beta-blockers are betaxolol (Kerlone) and nebivolol (Bystolic).
Beta2-Selective Beta-Blockers
Butoxamine is selective for beta-2 receptors. Since there is not an obvious medical use for this drug, it is only used for research purposes and is not available for medical use.
References
- "Basic and Clinical Pharmacology"; Bertram Katzung; 2007
- U.S. Pharmacist magazine: Nebivolol: New Beta-Blocker for Hypertension
