Labetalol’s Mechanism of Action: How Does It Work

Key takeaways:

• Labetalol is part of a group of prescription medications called beta blockers. It's FDA approved to treat high blood pressure (hypertension). It's the preferred beta blocker for hypertension in pregnancy and hypertensive emergencies.
• Labetalol's mechanism of action is to slow down your heart rate and widen your blood vessels. This lowers your blood pressure and helps reduce stress on your heart. It does this by blocking receptors (binding sites) in the body called beta and alpha receptors.
• Compared to other beta blockers, labetalol has a few differences. For example, it blocks alpha-1 receptors, but most other beta blockers don't. And it has to be taken 2 to 3 times a day in most cases, while other beta blockers can usually be taken 1 to 2 times a day.

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Nearly50% of adultsin the U.S. have high blood pressure (hypertension). This happens when the force of blood pushing against the walls of your blood vessels is too strong.

Hypertension doesn't usually cause noticeable symptoms, so many people don't know they have it. But if left untreated, it can cause major health issues such as heart disease, kidney disease, and even death.

Labetalolis one of severalprescription medicationsthat treats high blood pressure. But how exactly does it work to lower blood pressure? We'll go over labetalol's mechanism of action and the reasons you may be prescribed it.

What is labetalol?

Labetalol is abeta blockermedication that's FDA approved to treat hypertension. It's available in two forms: an oral tablet and an intravenous injection. The injection is only used by healthcare professionals in a hospital or similar setting. Labetalol tablets are only available in generic forms.

Labetalolisn't a first-choice medicationfor treating hypertension. Other medication groups - such as angiotensin-converting enzyme (ACE) inhibitors, angiotensin-II receptor blockers (ARBs), and thiazides - are typically tried before beta blockers. But if these medications aren't enough, beta blockers may be added on. Beta blockers may also be recommended if you have certain heart conditions along with hypertension.

However, labetalol is a first-choice medication forhypertensive emergencies. It's given intravenously for these situations. A hypertensive emergency is when you have extremely high blood pressure along with organ damage. Labetalol is also afirst-choice medication for hypertension in pregnancy.

How does labetalol work?

Labetalol works byblocking certain receptors(binding sites) throughout the body. These are called beta and alpha receptors.

Some beta blockers mainly block beta receptors in the heart. These are known as cardioselective beta blockers. Others block beta receptors throughout the body, such as the heart, blood vessels, and lungs. These are known as nonselective beta blockers. Labetalol falls into this category. It also blocks alpha receptors.

Let's dive into labetalol's mechanism of action and how it affects each type of receptor below.

Labetalol effect on beta-1 receptors

Labetalol blocksbeta-1 receptors. These are primarily found in three parts of the body: the heart, kidneys, and fat cells. In the heart, activating beta-1 receptors increases your heart rate and how strongly it contracts.

By blocking these receptors, labetalol slows your heart rate and makes it easier for your heart to pump blood to the rest of your body. This can lower blood pressure.

Labetalol effect on beta-2 receptors

Labetalol also blocksbeta-2 receptors. These are found throughout the body, such as in the blood vessels and muscles in the lungs, heart, and skin.

When beta-2 receptors are activated, your blood vessels dilate (widen) and yourheart contracts(tightens). When labetalol blocks these receptors, your blood vessels constrict (tighten)andyour heart rate slows.

Constricted blood vessels can make it harder for people with certain lung conditions to breathe, such as those with asthma or chronic obstructive pulmonary disease (COPD). So labetalolmay not be the best choicefor people with these conditions.

Labetalol effect on alpha-1 receptors

Labetalol is one of the few beta blockers that blocksalpha-1 receptors. When activated, alpha-1 receptorsconstrict your blood vesselsand increase your heart rate.

When labetalol blocks alpha-1 receptors, your blood vessels dilate and your heart rate slows. This decreases blood pressure.

Labetalol as an antioxidant

There's evidence that oxidative stress cannegatively affect your heart. Oxidative stress is when there aretoo many free radicals(unstable molecules that are harmful in large amounts) in the body. There's some evidence that labetalol mayreduce oxidative stress,giving it additional heart benefits. But we need more research on this topic, especially in humans.

Does labetalol start working immediately?

It depends on the form of labetalol you receive. The labetalol injection works almost immediately. The tablets may start workingwithin a few hours. But it typically takes 2 to 3 days for it to start lowering blood pressure.

How do you know if labetalol is working?

You may not have noticeable symptoms of hypertension. So you may not feel differently after taking labetalol.

Butchecking your blood pressure at homeis a way to see whether labetalol is working for you. Ask your prescriber how often they want you to check it, and what your goal blood pressure reading is.

It can take some time to find thelabetalol dosethat's right for you. If your dose is too low, your blood pressure may remain high. As mentioned, you might not have symptoms. Or you may feel headache, dizziness, and fatigue. If your dose is too high, your blood pressure may decrease too much. Symptoms oflow blood pressureto watch for include dizziness and weakness. This is common in the first few days after starting labetalol. But if it continues past a few days, or it feels severe, let your prescriber know.

Otherlabetalol side effects, such as fatigue and nausea, may also be more likely if your labetalol dose is too high. So keep your prescriber updated if you feel differently after starting labetalol.

How does labetalol compare to other blood pressure medications?

As mentioned, labetalol and other beta blockers typicallyaren't a first-choice optionfor treating high blood pressure. Typically, the medications listed below aretried first. These medications are known to be more effective at decreasing blood pressure and preventing long-term health problems compared to beta blockers:

However, beta blockers are a good option in some cases. For example, people with high blood pressureandother heart conditions may benefit from a beta blocker.

Compared to other beta blockers - such as metoprolol (Lopressor,Toprol XL),carvedilol(Coreg), andatenolol(Tenormin) - labetalol is unique in a few ways:

• It blocks alpha-1 receptors (and so does carvedilol). Most other beta blockers only block beta receptors.
• It's only approved to treat hypertension. Many other beta blockers are approved for other heart conditions.
• It needs to be taken more often (2 to 3 times a day) than most other beta blockers, which can be taken 1 to 2 times a day.
• It's the beta blocker of choice for hypertensive emergencies or hypertension in pregnancy. But it's not preferred for most other heart conditions. For example,metoprolol succinate or carvedilolare preferred beta blockers for heart failure.
• It may not be the best option for people with asthma. Other beta blockers like atenolol and metoprolol may be better options since they have less of an effect on blood vessels in the lungs.

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Münzel, T., et al. (2017).Impact of oxidative stress on the heart and vasculature: Part 2 of a 3-part series.Journal of the American College of Cardiology.

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Williamson, L. (2024).To curb high rates of heart disease and stroke, experts urge prevention and innovation. American Heart Association.

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