Overview of Beta Blockers

BETA BLOCKERS- GENERAL OVERVIEW
Propranolol (Inderal®) made its way to the American market in 1967. There are a bunch of beta-blockers available, and at least 10 different products sit on our community pharmacy shelves.  For the next few sessions, we will dissect the differences between these products.  In this session, we will discuss the most common uses and adverse effects of the beta blockers as a group.
Mechanism of Action
Beta blockers:

• suppress phase 4 depolarization
• Slows AV conduction
• Decreases heart rate
• Reduces sympathetic stimulation of the heart (beta-1).
• Slows sinus rhythm without significantly changing the QT or QRS interval
• Decreases myocardial oxygen demand

 
How do beta-blockers work…
This class of drugs works by antagonizing the neurotransmitters norepinephrine and epinephrine from binding to receptors—sympathetic stimulation (think of “fight or flight reflex”). There are three known types of beta receptors, known as beta1 (β1), beta2 (β2) and beta3 (β3).

• β1-adrenergic receptors are located commonly in the heart and kidneys.
  • Think of beta-blockers (Metoprolol, propranolol, etc)

• β2-adrenergic receptors are located mainly in the lungs, gastrointestinal tract, liver, uterus, vascular smooth muscle, and skeletal muscle.
  • Think of beta-2 agonists, such as albuterol for asthma

• β3- adrenergic receptors are located in fat cells, heart, and in the bladder.
  • Think of beta-3 agonist Mirabegron (Myrbetriq®)for overactive bladder

When the neurotransmitters are prevented from binding to the receptors, it blocks the effect of epinephrine/norepinephrine. This action allows the heart to relax and beat more slowly thereby reducing the amount of blood that the heart must pump. Over time, this action improves the pumping mechanism of the heart.
Common uses of beta blockers:

• Hypertension
• Arrhythmias: beta blockers are not pro-arrhythmic like many antiarrhythmic drugs (disopyramide, flecainide, propafenone, etc.)
• Systolic Heart Failure: increased survival
• Stable Angina: shows less anginal attacks
• Myocardial Infarction: improved survival
• Migraine Prophylaxis: show a 50% reduction in headaches
• Essential Tremor

Common side effects of Beta-Blockers:

• Fatigue
• Cold hands (due to decreased circulation)
• Depression (some studies do not show a link)
• Insomnia, Nightmares, Hallucinations
• Shortness of breath: increase airway resistance in patients with bronchospastic disease (COPD, Asthma), especially non-selective beta blockers.
• Bradycardia
• Heart failure: exacerbate heart failure in patients with decompensated heart failure
• Increased triglycerides
• Hyperkalemia- more of a problem with non-selective beta-blockers
• Decreased HDL
• Sexual dysfunction (some studies show minimal risk)
• May suppress reflex tachycardia in hypoglycemic events
• Weight gain (about 3 pounds) usually within the first few months of therapy)

Stopping Beta-Blockers:
Long term beta blocker therapy leads to an increase in receptor density.  This increase in receptor density may cause sudden withdrawal if the beta blocker is not tapered. This hypersensitivity to the catecholamines may precipitate angina, myocardial infarction and possibly lead to death.  This is especially a concern with short-acting beta blockers such as propranolol.

• Beta-blocker withdrawal should occur at a rate of 25% per week, taking 3-4 weeks.
• Be sure to have nitroglycerin up-to-date for angina patients.
• Monitor blood pressure (hypertensive crisis could occur)
• Remember, poor adherence to beta-blocker therapy could cause angina and hypertension.