Category:Beta blockers

Beta blockers（中文： β受體阻斷劑）

Beta blockers are competitive antagonists at beta-adrenergic receptors in a wide range of tissues. Blockade of beta receptors has the following effects:

• beta1 blockade mainly affects the heart, reducing heart rate, myocardial contractility, and rate of conduction of impulses through the conducting system. It also leads to suppression of adrenergic-induced renin release and lipolysis
• beta2 blockade leads to increased bronchial resistance and inhibition of catecholamine-induced glucose metabolism; there may also be an effect on heart rate. Beta2 blockade also appears to be the main mechanism for the reduction in intra-ocular pressure associated with beta blockers

Beta blockers are used in the treatment of hypertension, angina, cardiac arrhythmias, and myocardial infarction and also have a role in heart failurec. They are also used to control symptoms of sympathetic overactivity in the management of alcohol withdrawal, in anxiety disorders, in hyperthyroidism, and in tremor. Beta blockers are used in the prophylaxis of migraine. They are also used, with an alpha blocker, in the initial management of phaeochromocytoma. Some beta blockers are used as eye drops in the management of glaucoma and ocular hypertension.

Adverse Effects

Beta blockers are generally well tolerated and most adverse effects are mild and transient. The most frequent and serious adverse effects are related to their beta-adrenergic blocking activity. Among the most serious adverse effects are heart failure, heart block, and bronchospasm. Troublesome subjective effects include fatigue and coldness of the extremities; when beta blockers are used for long-term treatment of asymptomatic diseases such as hypertension, such effects may be an important determinant of patient compliance.

Cardiovascular effects include bradycardia and hypotension; heart failure or heart block may be precipitated or worsened in patients with underlying cardiac disorders. Abrupt withdrawal of beta blockers may exacerbate angina and may lead to sudden death

Bronchospasm, shortness of breath, and dyspnoea may be precipitated, particularly in patients with a history of obstructive airways disease, due to blockade of beta2 receptors in bronchial smooth muscle.

Beta blockers interfere with carbohydrate and lipid metabolism and can produce hypoglycaemia, hyperglycaemia, and changes in blood concentrations of triglycerides and cholesterol.

Precautions

• Beta blockers should not be given to patients with bronchospasm or asthma or to those with a history of obstructive airways disease.

• Other contra-indications include metabolic acidosis, cardiogenic shock, hypotension, severe peripheral arterial disease, sinus bradycardia, and second- or third-degree AV block; caution should be observed in first-degree block.

• Beta blockers may mask the symptoms of hyperthyroidism and of hypoglycaemia. They may unmask myasthenia gravis. Psoriasis may be aggravated.

• Beta blockers increase sensitivity to allergens and also the severity of anaphylactoid reactions.

• Abrupt withdrawal of beta blockers has sometimes resulted in angina, myocardial infarction, ventricular arrhythmias, and death. Patients on long-term treatment with a beta blocker should have their medication stopped gradually over a period of 1 to 2 weeks.

• Similar precautions apply when beta blockers are used as eye drops since systemic absorption can occur.

Interactions

Use of beta blockers with antiarrhythmic drugs and other drugs affecting cardiac conduction can precipitate bradycardia and heart block.

Sotalol is particularly prone to interactions with other drugs affecting cardiac conduction.

Beta blockers may potentiate bradycardia due to digoxin.