Focus on Pharmacology: Beta Blockers
One of the most common medication classes you’ll see in the clinical setting is the beta blocker. In this post we’ll talk about what they are, how they work, what conditions they’re used for and how you’re going to monitor your patient.
What are Beta Blockers?
Beta blockers are medications that have beta-adrenergic blocking properties, meaning they block sympathetic nervous system activity. They are mainly used to treat hypertension, but you will see a few other uses as well. Don’t worry, we’ll talk about these further on.
Where do Beta Blockers work?
The first thing to understand here is that there are two types of beta receptors in the body. Beta-1 receptors, which are present in the heart, and beta-2 receptors, which are present in vascular smooth muscle and the muscle lining the airways. Since beta-1 receptors are only present in the heart, when a drug is specific to beta-1 receptors it is often called “cardioselective.” Other beta blockers target both beta-1 and beta-2 receptors, so you may hear these referred to as “non-selective” as their effects are more widespread, with greater side effects as well.
What do Beta Blockers do?
Beta-1 adrenergic blockers, such as atenolol and metoprolol, exert their influence on the receptors located in the heart. By blocking sympathetic activity at the receptor site, they slow the heart rate and decrease contractile force, lowering the patient’s blood pressure. Beta blockers also cause decreased excretion of renin by the kidneys, which acts to lower blood pressure as well.
Propranalol is an example of a non-selective beta blocker. Because it can also affect the airways, propranalol (and other non-selective beta blockers) are avoided in patients with reactive airway disease such as asthma or COPD.
What conditions are Beta Blockers used for?
Beta blockers are used to treat more than just high blood pressure:
- Hypertension: Beta blockers are most commonly prescribed to treat hypertension.
- Angina: Decreasing the rate lowers myocardial oxygen demand. Decreasing blood pressure leads to a decrease in afterload, which decreases the workload of the heart, which also lowers myocardial oxygen demand. Need a refresher on angina? Common meds are atenolol, propranolol and metoprolol.
- Dysrhythmias: Beta blockers are often used to control the rate in atrial fibrillation. Expect to see esmolol, propranolol and maybe metroprolol used in this way.
- Myocardial infarction: When given within 24-hours of onset, beta blockers reduce cardiac workload and improve likelihood of survival. Common medications used for this purpose are atenolol, metoprolol, and propranolol.
- Heart failure: Beta blockers are used in coordination with other medications to slow the progression of heart failure. Metoprolol and carvedilol are the main ones used to slow the heart rate (giving the heart time to “rest” between beats) and lower blood pressure, which decreases afterload and, therefore, the workload of the heart.
- Migraines: Some beta blockers (such as atenolol, metoprolol, timolol and propranolol) are used to help prevent migraines by inhibiting arterial dilation in the brain.
- Glaucoma: Ophthalmic solutions are used to decrease eye pressures, though the mechanisms are not fully understood. Doses are generally not high enough to have a systemic effect, but if they do occur can include bronchoconstriction, hypotension and bradycardia. Timolol is one of the most commonly used beta blockers to treat glaucoma.
Drug Highlight: Metoprolol
Let’s take a deeper dive into the most common beta blocker you will see in the clinical setting: metoprolol. By now you’ve probably noticed that this class of drugs tends to end in “-olol.” While there are a few that do not, you can rely on this as a general rule of thumb. Metoprolol is typically prescribed to patients with hypertension, heart failure, angina and myocardial infarction. One interesting off-label use is as an anti-anxiety medication, in that it will combat the tachycardia and hypertension that typically accompany anxiety.
Metoprolol is a cardioselective beta blocker, meaning it just targets those beta-1 receptors in the heart. So, if your patient has asthma and you see that the new resident has prescribed her propranolol (which targets both beta-1 and beta-2 receptors), it might be a good idea to advocate for a cardioselective beta blocker such as metoprolol.
Metoprolol comes in a few different formulations: IV, tablet and extended-release tablet. A typical IV dose is 5mg q two minutes for up to three doses, while the extended release tablets range from 12.5 to 100mg (depending on what it’s being used for), and the regular tablets range from 25-100 mg per day in one or two doses (in general, of course).
How will you monitor your patient?
Because beta blockers lower the heart rate and blood pressure, you will need to monitor your patient for bradycardia and hypotension, including orthostatic hypotension. With that said, always get a blood pressure and heart rate prior to giving the dose. Most orders for metoprolol will have a hold parameter, meaning you’ll hold the medication if the heart rate is below 50 to 60 or the systolic blood pressure is below 90 or 100 (depends on the patient and MD’s orders).
You’ll also want to monitor your patient for the more common side effects such as fatigue, pulmonary edema, and congestive heart failure. Because one of the side effects is CHF, monitoring daily weights and intake/output is also important, as is assessing lung sounds, edema, O2 saturation and work-of-breathing.
What will you teach the patient?
- Teach patient how to count their pulse daily, preferably before taking their dose.
- Teach patient/family how to take blood pressure and how often (twice a week is a good general guideline).
- Teach patient to change positions slowly, from sitting to standing, from lying down to sitting or from lying down to standing.
- If the patient has diabetes, teach them that this medication can cause their blood sugar levels to increase.
- If the patient has diabetes, teach them that the beta blocker can mask the typical signs of hypoglycemia (does not block diaphoresis); they will need to monitor their blood glucose closely, especially if weakness or fatigue is present.
- Teach patients signs of pulmonary edema and congestive heart failure that should be reported to the MD (dependent edema, shortness of breath, wheezing, having to sleep propped up on pillows, etc…)
- Patient should not stop taking the medication abruptly as this can cause chest pain and rebound hypertension.
- If the patient is taking the medication for hypertension, teach them lifestyle modifications they can make to improve their blood pressure (weight loss, exercise, sodium restriction, smoking cessation).
TL;DR: Beta blockers block conduction at the AV Node, decrease heart rate and lower blood pressure. Watch your patient for bradycardia and hypotension. Typically you’ll hold for a HR below 50 or 60 and a BP below 90 or 100.
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