Adrenergic Antagonists: Beta Blockers

β  BLOCKERS

β-Receptor blockers have variable degrees of selectiv-ity for the β₁-receptors. Those that are more β₁ selec-tive have less influence on bronchopulmonary and vascular β₂-receptors (Table 14–3). Theoretically, a selective β₁-blocker would have less of an inhibi-tory effect on β₂-receptors and, therefore, might be preferred in patients with chronic obstructive lung disease or peripheral vascular disease. Patients with peripheral vascular disease could potentially have a decrease in blood flow if β₂-receptors, which dilate the arterioles, are blocked. β-Receptor blocking agents also reduce intraocular pressure in patients with glaucoma.

β-Blockers are also classified by the amount ofintrinsic sympathomimetic activity (ISA) they have. Many of the β-blockers have some agonist activity; although they would not produce effects similar to full agonists (such as epinephrine), β-blockers with ISA may not be as beneficial as β-blockers without ISA in treating patients with cardiovascular disease.

β-Blockers can be further classified as thosethat are eliminated by hepatic metabolism (such as metoprolol), those that are excreted by the kid-neys unchanged (such as atenolol), or those that are hydrolyzed in the blood (such as esmolol).