Beta Blockers

Beta blockers have a variety of effects on the heart including reduction of heart rate, decreased contractile force, and a lesser impulse conduction through the atrioventricular (AV) node. For these reasons, they are used for numerous cardiac conditions such as hypertension, angina pectoris, dysrhythmias, myocardial infarction, and heart failure. Beta blockers that treat cardiac dysrhythmias, such as propranolol will be covered later in this module under the dysrhythmia category.

Prototype and Other Medications

This section discusses two beta blockers that treat hypertension, as the prototype medications for this category. They are atenolol and metoprolol. These are second-generation beta blockers that selectively block beta₁ receptors. Other medications in this category include the cardioselective beta blockers esmolol, acebutolol, betaxolol, bisoprolol, and nebivolol, which are beta₁ selective blockers. Nonselective beta blockers bind to both beta₁ and beta₂ receptors and include propranolol, carvedilol, labetalol, nadolol, pindolol, sotalol, and timolol. Some of the nonselective beta blockers also work as antiarrhythmic class II medication.

Expected Pharmacologic Action

Beta₁ blockers exert their antihypertensive effects in an indirect manner because they primarily affect the heart and kidney. In the heart, they block the beta₁receptors, which causes a decrease in heart rate and contractility. This decreases cardiac output and suppresses reflex tachycardia. In the kidney, they block renal Beta₁receptors, causing a decrease in the release of renin. This decreases angiotensin-I-related vasoconstriction, as well as aldosterone-related fluid retention. Beta₁blockers also decrease peripheral resistance of blood vessels by an unknown mechanism.

Adverse Drug Reactions

Bradycardia is an adverse drug reaction of beta blockers, due to the blockade of beta₁ receptors. This may lead to reduced cardiac output. Heart failure, due to reduced contractility of the heart, can also occur. This results in shortness of breath, edema, and coughing, especially at night when the client is lying flat. Sudden withdrawal of a beta blocker from a client with coronary heart disease, often abbreviated CHD, can cause rebound excitation. This causes anginal pain or a myocardial infarction.

Interventions

When caring for clients taking a beta blocker, monitor their heart rate and report to the provider a rate that is less than 50 beats per minute, or lower than a client-specific prearranged parameter. Be sure to monitor for signs of heart failure, such as shortness of breath, peripheral edema of the extremities, and night cough, and report them to the provider. Instruct clients not to stop their beta blocker suddenly, and if they do need to discontinue their medication, it must be done slowly by tapering the medication over 1 to 2 weeks.

Administration

All beta blockers are available orally, and several, including atenolol and metoprolol, are also available for intravenous use. Give them orally for hypertension, and both orally and intravenously for acute myocardial infarction. Atenolol is available in a tablet, which may be crushed or swallowed. Metoprolol is available as an immediate-released tablet or in a sustained-release dose which the client must swallow whole, not crushed. Absorption of metoprolol may be enhanced with food. The client must take it at the same time every day. The best time to take atenolol is before meals, or at bedtime.

Client Instructions

Instruct clients taking a beta blocker to check their pulse rate daily before taking the medication. Tell them to report to the provider a pulse that is less than 60 beats per minute, or lower than a client-specific prearranged parameter. Warn clients not to stop taking this medication abruptly. If they want to discontinue the medication, they must first talk to their provider so it is done properly, and the provider can prescribe another medication. Instruct clients who have a history of angina to report an increase in angina, or new onset of chest pain, to their provider. Instruct clients to report shortness of breath, peripheral edema of the extremities, and night coughing to the provider, as these are signs and manifestations of heart failure.

Safety Alert

Clients on beta blockers and other medications that can cause decreased cardiac output must know the signs of heart failure. The manifestations they experience will depend on whether the failure involves the right or left side of the heart. Left-sided failure allows blood to back up into the lungs so the signs and manifestations include dyspnea, cough that is worse at night, increased rate of respirations, crackles in the lungs upon auscultation, fatigue, and pallor. Right-sided failure allows blood to back up into the body so the signs and manifestations include jugular venous distension seen in the neck, dependent edema of the lower extremities, abdominal distension, nocturia, and weight gain from retained fluids. Clients must know the signs and manifestations of both right and left-sided heart failure when taking a beta blocker and report them to the provider if they occur.

Contraindications and Precautions

Do not give beta blockers to clients who have sinus bradycardia, or greater than a first-degree heart block, moderate to severe heart failure, or cardiogenic shock. The effects of beta-adrenergic blockers cause a decrease in rate and contractility of the heart. Do not use atenolol with clients who have peripheral vascular disease, or Raynaud’s disease. Don’t give metoprolol to children less than 6 years of age. Use beta blockers with caution, in clients whose heart failure is being controlled by digitalis and diuretics, clients who have asthma, chronic obstructive pulmonary disease (COPD), or other chronic respiratory disorders. Also use them with caution in clients who have a renal or liver disorder, myasthenia gravis, hyperthyroidism, diabetes mellitus, major depression, or pheochromocytoma, a type of adrenal gland tumor.

Interactions

Using beta blockers with other antihypertensive medications may increase their antihypertensive effects. Their use with digoxin will have an additive effect and may increase bradycardia. Antacids may decrease the absorption of beta blockers. Giving beta blockers with oral hypoglycemic agents may increase a client’s risk for hypoglycemia. Beta blockers may also increase the effects of neuromuscular blockers. Both antimuscarinic and anticholinergic medications may decrease the effects of beta blocker medications.