Adverse Reactions to β 2-Agonist Bronchodilators

Abstract

β₂-Agonists are safe and effective bronchodilator drugs. Their major adverse effects of skeletal muscle tremor, tachycardia and various metabolic effects are mediated by β-adrenoceptor stimulation and are reversible. Skeletal muscle tremor is the most frequent dose-limiting side effect. It may be reduced by commencing treatment with a low dose and if it persists another β₂-agonist may be tried. Other side effects such as cardiac arrhythmias and reduction in PaO2 are a serious potential problem in some susceptible asthmatics. However, they are infrequent or of a mild degree and are generally outweighed by the good control of asthma produced by β₂-agonists. Side effects from β₂-agonist therapy can be minimised by use of the inhaled route which selectively delivers the drug to the airways. Furthermore, selective tolerance develops to their side effects. The dose of a β₂-agonist should be assessed on the basis of therapeutic effect and the level of tolerance to its side effects. Recommended doses of β₂-agonists used for long term therapy do not cause clinically significant desensitisation of airway β-adrenoceptors, although this may become a relevant problem in patients who are regularly receiving very high doses. Intravenous β₂-agonists have a place in the treatment of severe asthma not responding to nebuliser therapy. In this life-threatening situation with severe airflow obstruction, monitoring of heart rate, PaO₂, plasma potassium and the electrocardiogram should be mandatory and supplemental oxygen given so that serious adverse effects are prevented.