Pharmacology/Beta - blockers

Definition
Beta blockers, also known as beta antagonists, are a class of drugs that were first developed for the treatment of certain heart conditions and hypertension. Later, beta blockers were also found to be useful in glaucoma, migraine, and some psychiatric disorders such as performance anxiety, tremors secondary to lithium, and movement disorders that are caused by some drugs used in the treatment of psychosis. In the United States, the most commonly used beta blocker used in psychiatric practice is propranolol (Inderal). Nadolol (Corgard), metoprolol (Lopressor), and atenolol (Tenormin) are also used in psychiatric practice but to a lesser degree.

Purpose

Beta blockers are proven effective in the treatment of performance anxiety, lithium-induced tremor, and neuroleptic-induced akathisia (a physical condition caused by certain antipsychotic drugs). Beta blockers have sometimes been used with benzodiazepines in treating alcohol withdrawal.

Description

Beta blockers act on that part of the central nervous system that controls mental alertness, lung function, heart rate, and blood vessels. Although there is more than one mechanism by which beta blockers work in anxiety states, the most beneficial result probably arises from the fact that beta blockers slow the heart to a normal rate and rhythm. Therefore, persons with performance anxiety do not experience the usual chest tightness and rapid heart rate that is associated with such acts as public speaking or acting.

Certain antipsychotic medications known as neuroleptics can cause an unwanted effect called akathisia, which is the inability to sit, stand still, or remain inactive. Patients are restless, and in severe cases, may pace constantly and forcefully and repeatedly stomp their feet. Beta blockers can sometimes treat this condition with a lower incidence of side effects than any other drugs used to treat this condition.

Propranolol is available in 10- to 90-mg tablets. Nadolol is available in 20-, 40-, 80-, 120-, and 160-mg tablets. Atenolol is available in 50- and 100-mg tablets. Metoprolol is available in 50- and 100-mg tablets.

Recommended dosage

For the treatment of performance anxiety, sometimes called stage fright, a single dose of propranolol ranging from 10–40 mg is given 20–30 minutes before the event causing the unwanted reactions.

For lithium-induced tremors that cannot be controlled by reducing caffeine intake or administering the dosage of lithium at bedtime, propranolol at a dose of 20–160 mg daily can be given in two or three evenly divided doses.

For akathisia caused by antipsychotic medications, propranolol can be administered at doses of 10–30 mg three times daily.

Precautions

Because of their ability to narrow airways, beta blockers, especially propranolol, should not be taken by people with asthma and chronic obstructive pulmonary disease (COPD). If there is an urgent need to use beta blockers in persons with respiratory problems, atenolol or metoprolol are the beta-blockers of choice because they are less likely to have this side effect, although even these drugs should also be used with caution. Patients with congestive heart failure or certain cardiac conduction abnormalities such as a heart block, should also receive these drugs with caution.

Beta blockers should be used with close physician monitoring in people with diabetes, since the symptoms of low blood sugar (increased heart rate, lightheadedness, and abnormal perspiration) may be not be recognized by patients.

Side effects

Beta blockers can cause undesired decreases in blood pressure and are typically not given if blood pressure is 90/60 mm Hg or less.

Beta blockers can also cause an undesired drop in heart rate. People whose resting heart rate is less than 55 beats per minute should not take beta blockers.

Occasionally, beta blockers can cause heart depression, bronchoconstriction, impotence, fatigue, depression, bradycardia, rash, weakness, nausea, vomiting, and stomach discomfort.

Beta blockers should be discontinued by patient to reduce the likelihood of angina.

Interactions

Each medication in the class of beta blockers has the potential to interact with a multitude of other medications. Anyone starting beta blocker therapy should review the other medications they are taking with their physician and pharmacist for possible interactions. Patients should always inform all their health care providers, including dentists, that they are taking beta blockers.

'BOOKS' Kaplan, Harold. Comprehensive Textbook of Psychiatry. Philadelphia: Lippincott Williams and Wilkins, 1995.

Kay, Jerald. Psychiatry: Behavioral Science and Clinical Essentials. Philadelphia: W. B. Saunders Company, 2000.

Ajna Hamidovic, Pharm.D.