Beta Blocks what are they and what do they do?

“Beta-blockers are drugs that bind to beta-adrenoceptors and thereby block the binding of norepinephrine and epinephrine to these receptors. This inhibits normal sympathetic effects that act through these receptors. Therefore, beta-blockers are sympatholytic drugs. Some beta-blockers, when they bind to the beta-adrenoceptor, partially activate the receptor while preventing norepinephrine from binding to the receptor. These partial agonists therefore provide some “background” of sympathetic activity while preventing normal and enhanced sympathetic activity. These particular beta-blockers (partial agonists) are said to possess intrinsic sympathomimetic activity (ISA). Some beta-blockers also possess what is referred to as membrane stabilizing activity (MSA).  This effect is similar to the membrane stabilizing activity of sodium-channels blockers that represent Class I antiarrhythmics.

The first generation of beta-blockers were non-selective, meaning that they blocked both beta-1 (β₁) and beta-1 (β₂) adrenoceptors. Second generation beta-blockers are more cardioselective in that they are relatively selective for β₁ adrenoceptors. Note that this relative selectivity can be lost at higher drug doses. Second generation beta-blockers are more cardioselective in that they are relatively selective for β₁ adrenoceptors. Note that this relative selectivity can be lost at higher drug doses. Finally, the third generation beta-blockers are drugs that also possess vasodilator actions through blockade of vascular alpha-adrenoceptors.

Because there is generally some level of sympathetic tone on the heart, beta-blockers are able to reduce sympathetic influences that normally stimulate chronotropy (heart rate), inotropy (contractility), dromotropy (electrical conduction) and lusitropy (relaxation). Therefore, beta-blockers cause decreases in heart rate, contractility, conduction velocity, and relaxation rate.

Used to Treat:

• Hypertension (HTN)
• angina
• myocardial infarction
• arrhythmias
• heart failure

Beta-Blockers

Cardiac Effects

• Decrease contractility
  (negative intropy)
• Decrease relaxation rate
  (negative lusitropy)
• Decrease heart rate
  (negative chronotropy)
• Decrease conduction velocity
  (negative dromotropy)

Vascular Effects

• Smooth muscle contraction
  (mild vasoconstriction)

Beta Blocker List

Betapace (sotalol)   Non-selective β₁/β₂

Blocardren (Timolol)  Non-selective β₁/β₂

Brevibloc (Esmolol)  β₁-selective

Corgard (Nadolol)  Non-selective β₁/β₂

Coreg (Carvedilol)  Non-selective β₁/β₂

Inderal (Propranolol)  Non-selective β₁/β₂

Kertone (betaxolol)  β₁-selective

Lopressor (Metoprolol)  β₁-selective

Normodyne (Labetalol)  Non-selective β₁/β₂

Sectral (acebutolol)   β₁-selective

Tenormin (Atenolol)  β₁-selective

Toprol (Metoprolol)  β₁-selective

Zebeta (Bisoprolol)  β₁-selective

Ziac (Bisoprolol + HCTZ)  β₁-selective + Hydrochlorothiazide (diuretic)

Side Effects

Cardiovascular

• bradycardia
• reduced exercise capacity
• heart failure
• hypotension,
• atrioventicular (AV) nodal conduction block.

Other

• Bronchoconstriction  (non selective)  Contraindicated in asthma
•  Hypoglycemia (β₂-adrenoceptors normally stimulate hepatic glycogen breakdown (glycogenolysis) and pancreatic release of glucagon, which work together to increase plasma glucose)

Source: http://www.cvpharmacology.com/cardioinhibitory/beta-blockers.htm