Beta-blockers, also known as beta-receptor blockers or beta-adrenoreceptor antagonists, are a group of drugs that inhibit the action of the catecholamines epinephrine and norepinephrine in the body.
What are beta blockers?
In arterial hypertension, beta-blockers are often prescribed in combination with other antihypertensive agents, for example diuretics. These two transmitter substances, also known as “stress hormones,” bind to the ß-receptors of various organs in the body, triggering processes that are sometimes physiologically important and sometimes pathological. Beta-blockers have similar chemical structural components to epinephrine and norepinephrine, which allows them to occupy their receptors as competitive antagonists without triggering the corresponding effects. They can be broadly divided into ß1-selective and non-selective beta-blockers. The former are characterized by higher cardiac selectivity because the density of the ß1 receptor subtype is particularly high at the heart. This is a desired property in most indications; examples of active ingredients are atenolol, bisoprolol, metoprolol, and nebivolol. The nonselective beta-blockers such as propranolol, timolol, and sotalol have been shown to be effective in other indications.
Medical effects and use
The most common medical use of beta-blockers relates to the cardiovascular system. By blocking ß-receptors, beta-blockers decrease the contractility and excitability of the heart as well as its beating rate, resulting in a drop in blood pressure. In arterial hypertension, beta-blockers are often prescribed in combination with other antihypertensive agents, for example diuretics. In contrast to the drug groups of ACE inhibitors, diuretics and AT1 antagonists, ß1-selective beta blockers such as metoprolol can also be used in pregnancy. Beta-blockers are also prescribed for coronary artery disease, heart failure, arrhythmias, and myocardial infarction prophylaxis. Beta-blockers also decrease aqueous humor production in the eye by lowering aqueous humor secretion and can therefore also be used to treat glaucoma (timolol). Metoprolol and propranolol are also used as first-line agents for migraine prophylaxis. Other indications include hyperthyroidism, tremor, and pheochromocytoma, a catecholamine-producing tumor of the adrenal gland.
Interactions
Most beta-blocker interactions involve their antihypertensive effects and their potentiation by other agents. If acetylcholinesterase inhibitors such as rivastigmine, donepezil, and galantamine (agents used to treat Alzheimer’s dementia) are taken during beta-blocker therapy, bradycardia (lowered heart rate) and bronchoconstriction with shortness of breath may result from mutual potentiation of effects. Simultaneous treatment with other antihypertensive drugs and the antiarrhythmics amiodarone and dronedarone can also result in an increased drop in blood pressure and bradycardia. If co-medication with the above agents cannot be avoided, heart rate and blood pressure should be monitored and dosages adjusted as necessary. Diabetics treated with insulin or sulfonylureas such as glibenclamide may experience increased hypoglycemia. Furthermore, the warning symptoms of hypoglycemia, such as agitation, headache, tremor, and tachycardia, are masked. In particular, the nonselective beta-blockers may partially abolish the bronchodilator effect of theophylline and its derivatives, resulting in respiratory distress.
Risks and Side Effects
Beta-blockers should generally be dosed gradually in and out to avoid side effects. This means that low doses are taken at the beginning of therapy and the dosage is increased slowly; abrupt discontinuation should also be avoided. Possible side effects occur mainly at the start of treatment with beta-blockers and include an excessive drop in blood pressure, dizziness, fatigue, nervousness, sleep disturbances, bradycardia, sweating, gastrointestinal complaints, muscle weakness, edema, and impotence. Beta-blockers should not be used in severe peripheral circulatory disorders, severe asthma, low blood pressure, and bradycardia; special monitoring is needed in diabetes mellitus and renal insufficiency. After careful risk-benefit assessment, beta-blockers can be used in pregnancy, but should be discontinued 72 hours before term to avoid bradycardia in the newborn.Athletes should note that beta-blockers are assigned to the doping list substance classes prohibited for certain sports.
