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).
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