Beta blockers: Cardiac jacks of all trades

Uses for beta blockers range from lowering blood pressure to improving heart failure.

The release of the first beta blocker in the early 1960s revolutionized the treatment of chest pain caused by exertion or stress (angina). Over the following four decades, these old dogs have learned many new tricks, from protecting the heart after a heart attack to controlling heart failure. Today, millions of Americans take a beta blocker.

This medication spotlight looks at how beta blockers work, who can benefit from them, and what to expect if you take one.

What beta blockers do

Tiny proteins called beta receptors sit on the outer surface of many cells. There are three main types. Beta-1 receptors are found almost exclusively in heart cells. Beta-2 receptors reside mostly in lung and blood vessel cells, though heart cells also have some. Beta-3 receptors are located on fat cells.

The job of beta receptors is to latch onto chemical messengers released by the nervous system. In response to these messengers, the heart beats faster, blood vessels constrict, the airways relax, and the kidneys increase production of a protein that boosts blood pressure.

Beta blockers subvert these processes by settling onto beta receptors and preventing the chemical messengers from binding to their receptors. That slows the heart, improves the conduction of electrical signals in the heart, relaxes blood vessels, and lowers blood pressure.

Who needs a beta blocker?

Beta blockers are used for many reasons, including:

• angina

• cardiac healing after a heart attack

• heart failure

• heart rhythm problems such as atrial fibrillation or palpitations

• high blood pressure

• hypertrophic cardiomyopathy

• noncardiovascular conditions such as anxiety, essential tremor, glaucoma, migraine, and others.

Once a mainstay for treating high blood pressure, beta blockers have been elbowed aside by newer drugs, such as ACE inhibitors, and older ones, such as thiazide diuretics.

A bunch of beta blockers

You can tell a beta blocker by its generic name — they all end in "lol." Each has its own particular way of blocking beta receptors. This accounts for their different actions and side effects.

More than a dozen beta blockers have been approved for use in the United States (see table). They fall into three main groups.

Nonselective. The earliest beta blockers, like propranolol, affect both beta-1 and beta-2 receptors. Nonselective beta blockers should be used with caution, if at all, in smokers or people with asthma or other lung conditions.

Cardioselective. A number of beta blockers, including atenolol (Tenormin) and metoprolol (Toprol, Lopressor), were designed to block only beta-1 receptors in heart cells. Since they don't affect beta-2 receptors in blood vessels and the lungs, cardioselective beta blockers are safer for people with lung disorders.

Third-generation. Some beta blockers do more than block beta receptors. Labetalol (Normodyne, Trandate) blocks alpha receptors, too. This further helps relax blood vessels. Nebivolol (Bystolic) stimulates the inner lining of blood vessels (the endothelium) to generate nitric oxide, which helps the vessels relax. Carvedilol (Coreg) does both.

Effective, safe, inexpensive

Analyses of beta blockers by the independent Drug Effectiveness Review Project at Oregon Health & Science University and by Consumers Union, publishers of Consumer Reports, evaluated beta blockers for effectiveness, safety, and cost.

Effectiveness. The Oregon researchers found compelling evidence that taking a beta blocker after having had a heart attack lowers the chances of a repeat heart attack or an early death. These drugs also increase the chances of living longer and better with heart failure. The reviewers found that different beta blockers work better for different conditions.

Safety. Beta blockers are generally safe to take. Side effects tend to be annoying, not life-threatening. Doctors long withheld beta blockers from people with chronic obstructive pulmonary disease over worries that these drugs would worsen symptoms, but a report in the Archives of Internal Medicine showed that judicious use of beta blockers may decrease flare-ups of this common breathing problem and improve survival.

Cost. Almost all beta blockers are available as low-priced generics.

Which one is right for you depends on the reason you need it, your other cardiovascular and medical conditions, and side effects. As part of its Best Buy Drugs series, Consumer Reports offers recommendations based on effectiveness, safety, and cost. You can download the report at health.harvard.edu/176.

Taking a beta blocker

How often you take a beta blocker depends on the medication. Some are once-a-day, extended-release pills; others must be taken in the morning and in the evening. As with every medication and supplement you take, talk with your doctor or nurse if you have questions.

Starting a beta blocker isn't like starting aspirin or many other drugs, with everyone taking the same dose. It's important to start at a low dose and gradually work your way upward. Starting with too large a dose right off the bat could lower your heart rate and your blood pressure into dangerous territory.

You need to be just as careful stopping a beta blocker as starting one. Quitting suddenly can cause what is known as "rebound angina." It can also, though very rarely, trigger a heart attack, stroke, or erratic heart rhythm. Gradually decreasing the dosage can help prevent these problems.

Side effects

If beta receptors existed only in heart cells, beta blockers would be a more ideal cardiac drug. But since beta receptors are found in so many other tissues, these drugs can have unwanted effects throughout the body. That beta blockers have been in use for half a century is a plus, because it has given doctors and researchers plenty of time to observe how well these medications work, how safe they are, and what side effects they cause.

Most people who take a beta blocker experience at least one side effect from the drug. Although these are usually tolerable, about one in five people ends up switching to a different beta blocker or to another type of drug because of side effects. The most common ones include

• drowsiness or fatigue

• weight gain

• shortness of breath or difficulty breathing

• tingling or coldness in the hands or feet

• dizziness or lightheadedness

• headache

• trouble sleeping or disturbing dreams

• upset stomach, constipation, or diarrhea

• mild depression

• lowered sex drive.

The lower the dose, the lower the chances that a beta blocker will cause noticeable side effects. The combination of individual differences and medication differences means it can be a balancing act to find the drug and dosage that work best with the fewest side effects. If a side effect appears, don't be too quick to switch — adverse effects sometimes go away as the body gets used to the drug. If it persists, changing to a different beta blocker can often take care of the problem.