Clinical differences between beta-adrenergic blocking agents: Implications for therapeutic substitution

Abstract

The beta blockers exhibit clinically significant differences in beta-receptor selectivity, intrinsic sympathomimetic activity, and alpha-adrenergic blocking activity. These agents also show important differences in their pharmacokinetic profiles, including gastrointestinal absorption, first-pass hepatic metabolism, lipid solubility, protein binding, hepatic biotransformation, pharmacologic activity of metabolites, and renal clearance of unchanged drug and metabolites. These many differences determine the appropriateness of administering a given beta blocker in a given clinical situation. The selection of beta blockers must also take into account concurrent therapy with other agents. Concurrent administration of beta blockers with drugs that alter gastric, hepatic, or renal function may affect blood levels, duration of action, or efficacy of beta-blocker action. The beta blockers vary in the extent to which their action is altered when they are given with other agents, and therapeutic substitution may produce unwanted side effects and toxicity. Elderly patients should be carefully monitored following interchange among beta blockers, since the probability of drug interaction, impact of adverse effects, unpredictability of response, and physiologic variability of renal and liver function is greater than for younger individuals. Therapeutic substitution among beta blockers in patients already stabilized on a given agent will require careful monitoring. Retitration with the new beta blocker will be required in many cases to assure therapeutic equivalence. Beta blockers are currently used for over 20 medical conditions. There is wide variation in the strength of the clinical evidence supporting the use and efficacy of specific beta blockers for specific conditions. Substitution of one beta blocker for another should be based on published evidence of efficacy in treating the condition for which it is being used. Detailed knowledge of the medical history, physical examination findings, laboratory test results, and diagnosis is essential for rational selection of a beta blocker. The expense of retitration, of more freqjent patient monitoring, and of hospitalization due to adverse or subtherapeutic effects must be weighed against any cost savings achieved through therapeutic substitution of these agents. The actual clinical and economic effects consequent to therapeutic substitution between beta blockers have not yet been measured. Such assessment is necessary before the medical community can sanction this practice.