What are Beta-Blockers?

Beta-Blockers Introduction

Beta-blockers are among some of the most widely prescribed medicines. Working in the pharmacy, you will handle beta-blockers daily. As such, it’s important that you have a working knowledge of what they are and how they work.

In 1964, beta-blockers were first synthesized by Sir James Black, a Scottish doctor and pharmacologist. This discovery transformed the way in which conditions, such as angina pectoris, were managed. However, since then, beta-blockers have found use in a wide variety of other conditions.

These include:

• Ischemic heart disease – first-line agents to improve symptoms and prognosis linked to angina and ACS, acute coronary syndrome.
• Chronic heart failure (CHF) – first-line agent to improve prognosis.
• Atrial fibrillation (AF) – first-line agent to reduce ventricular rate. In the case of paroxysmal AF, they are used to maintain sinus rhythm.
• Supraventricular tachycardia (SVT) – again, to restore sinus rhythm (in patients without circulatory compromise).
• Hypertension – they are not first-line agents to treat high blood pressure. Instead, thiazide diuretics or calcium channel blockers are preferred. However, beta-blockers may be used when other medicines prove insufficient in managing the condition.

To understand why beta-blockers are used to treat these conditions, we must understand the pharmacology of beta-blockers – namely, how they work.

Mechanism of Action

At the most fundamental level, beta-blockers work by blocking the effects of epinephrine and norepinephrine on adrenergic beta receptors. Epinephrine is responsible for the “fight-or-flight” response.

There are three types of beta receptor – beta-1, beta-2, and beta-3.

Some drugs block one receptor subtype, whereas other beta-blockers block all three receptor subtypes. Depending on which beta receptor is blocked, that determines what clinical function the drug will have.

Where are beta receptors located?

• Beta-1 receptors: primarily in the heart and kidneys
• Beta-2 receptors: vascular smooth muscle, skeletal muscle, uterus, lungs, and the gastrointestinal tract
• Beta-3 receptors: fat cells

In the case of angina, then, we can see that beta-1 receptor blockade is responsible for reducing the force of contraction and speed of conduction of the heart. This reduces cardiac work and oxygen demand. This is the same reason why beta-blockers are effective in the treatment of chronic heart failure.

Examples of beta-1 selective blockers include:

• Atenolol
• Metoprolol
• Nebivolol
• Esmolol

Non-selective beta-blockers (who block any of the above receptors) include:

• Propanolol
• Labetalol
• Carvedilol
• Pindolol

As you may have noticed, beta-blockers can be identified via the suffix -lol. If, in the PTCB exam, you are asked to identify the beta-blocker from a list of medicines, this is how you should know the answer.

What about the other indications? In the case of atrial fibrillation, these drugs prolong the refractory period of the atrioventricular node (AV) – restoring and maintaining sinus rhythm.

Beta-blockers reduce hypertension by reducing renin secretion from the kidney, as this process is mediated by beta-1 receptors.

Side Effects

Though this is not a complete list, side effects include:

• Cold extremities
• Reynaud’s phenomenon
• Headache
• GI effects – nausea, vomiting
• Vivid dreams and/or nightmares
• Impotence
• Hypotension
• Alteration in glucose and lipid metabolism
• Weight gain

Beta-blockers can induce bronchospasm and so should be avoided in asthma. Furthermore, beta-blockers can mask the effects of hypoglycemia, which is an important consideration in patients with diabetes.

We learned above that beta-blockers are not routinely used in treating hypertension. Instead, thiazide diuretics and calcium channel blockers are preferred for this purpose.

Calcium channel blockers include drugs such as verapamil and diltiazem, but neither of these drugs should be taken alongside a beta-blocker, as the combination can precipitate heart failure, bradycardia, and asystole.

Final Thoughts

Knowing the pharmacology of beta-blockers is important. These are widely used medicines in the pharmacy setting and, as a prospective pharmacy technician, you should have a rounded and basic understanding of these medicines.

You need to know:

• What beta-blockers are typically used to treat?
• How you can identify if a medicine is a beta-blocker?
• How beta-blockers work and what side-effects are they linked to?

If you can answer all three questions, you will have no problem on the day of your PTCB exam.

If you’d like to test your knowledge with our PTCB practice exams, become a registered member of PTCB Test Prep today.