Pharmacological characteristics of beta blockers and their role in clinical practice

Since beta-adrenoceptor blocking drugs were originally discovered and shown to be important therapeutic agents in the management of both angina pectoris and hypertension, many other similar drugs have become available. These share the common property of beta-adrenoceptor antagonism, though they may vary in terms of potency. However, they differ from one another in terms of their additional pharmacological properties--cardioselectivity, partial agonist activity, and membrane stabilizing activity. Cardioselectivity refers to the ability of some drugs, notably atenolol and metoprolol, to block beta 1 receptors without blocking beta 2 receptors. This has been considered to be of potential importance in patients with obstructive airways disease, patients with peripheral vascular disease, and patients with insulin-dependent diabetes during hypoglycemic crisis. Partial agonist activity is the intrinsic activity that some drugs have to stimulate the beta adrenoceptor while they are competitively antagonizing catecholamines. In consequence, they may have less effect on resting heart rate, cardiac output, peripheral vascular blood flow, and resting respiratory function. However, there is no good evidence that major adverse effects of beta-adrenoceptor blocking drugs such as congestive heart failure, bronchospasm, or symptoms of peripheral vascular disease are prevented by drugs with partial agonist activity: bradycardia may be improved, but its importance has probably been overemphasized. Membrane-stabilizing activity appears to be unimportant. As far as pharmacokinetic differences between drugs are concerned, lipid solubility is seen to be of increasing importance. The more water-soluble drugs have longer elimination half-lives, produce less interindividual variation in steady-state plasma concentrations, and penetrate the central nervous system less readily.(ABSTRACT TRUNCATED AT 250 WORDS)