Selective β1 antagonists Drugs that preferentially block the β1 receptors have been developed to eliminate the unwanted bronchoconstrictor effect (β2 effect) of propranolol seen among asthmatic patients. Cardioselective β-blockers, such as acebutolol [a-se-BYOO-toelole], atenolol [a-TEN-oh-lole], and metoprolol [me-TOE-proe-lole], antagonize β1 receptors at doses 50- to 100-fold less than those required to block β2 receptors. This cardioselectivity is thus most pronounced at low doses and is lost at high doses. [Note: Acebutolol has some intrinsic agonist activity.
1. Actions: These drugs lower blood pressure in hypertension and increase exercise tolerance in angina . Esmolol [EZ-moe-lole] has a very short lifetime due to metabolism of an ester linkage. It is only given intravenously if required during surgery or diagnostic procedures (for example, cystoscopy). In contrast to propranolol, the cardiospecific blockers have relatively little effect on pulmonary function, peripheral resistance, and carbohydrate metabolism. Nevertheless, asthmatics treated with these agents must be carefully monitored to make certain that respiratory activity is not compromised
2. Therapeutic use in hypertension: The cardioselective β-blockers are useful in hypertensive patients with impaired pulmonary function. Because these drugs have less effect on peripheral vascular β2 receptors, coldness of extremities, a common side effect of β-blocker therapy, is less frequent. Cardioselective β-blockers are useful in diabetic hypertensive patients who are receiving insulin or oral hypoglycemic agents.