Do we need a new classification of beta-blockers?

Abstract

Beta-adrenoceptor blocking drugs (beta-blockers) first came into clinical use 25 years ago. Initially, propranolol was the only beta-blocker available but a number of others, similar in chemical composition and action, became available in the following 10 years. Most blocked both beta 1- and beta 2-receptors and differed only in that some possessed membrane stabilising activity and some were partial agonists. These properties, which were the only pharmacological differences between many beta-blockers, were not found to be clinically very relevant. The main problems associated with the use of beta-blockers were caused by their unwanted effects on beta 2-receptors. The potential to prevent sympathetically-mediated bronchodilatation and thereby cause bronchospasm was, and is, the adverse effect causing most concern. The advent of relatively beta 1-selective beta-blockers, in particular metoprolol and atenolol, made it possible to achieve the therapeutic benefits of beta 1-blockade whilst reducing the unwanted effects of beta 2-blockade; which, in addition to causing less bronchospasm, also meant less impact on arterial vasodilatation and insulin, glucose and free fatty acid release. Unfortunately, beta 1-selective drugs reduce, but do not eliminate, the unwanted effects of beta 2-blockade and the larger the dose and the higher the plasma and tissue concentrations, the greater the effect on beta 2-receptor sites. Drugs which may act as beta-blockers at beta 1-receptor sites whilst having some, albeit mild, stimulatory action at beta 2-receptors are now available.(ABSTRACT TRUNCATED AT 250 WORDS)