The use of beta-agonists and the risk of death and near death from asthma

Nebulized fenoterol causes greater cardiovascular and hypokalaemic effects than equivalent bronchodilator doses of salbutamol in asthmatics

The pulmonary and extrapulmonary effects of two doses of nebulized fenoterol (5 mg) salbutamol (5 mg) and ipratropium bromide (0.5 mg) at 60 min intervals were compared in nine patients with asthma in a double-blind, randomized study. Measurements of heart rate, blood pressure, electromechanical systole (QS2I), QTc interval, FEV1 and plasma potassium were made at baseline and at 15, 30 and 60 min after each nebulization. Both beta-agonists caused significantly greater inotropic (QS2I), chronotropic (HR), electrocardiographic (QTc) and hypokalaemic effects than ipratropium bromide (IB), with fenoterol being more potent than salbutamol. Fenoterol had no greater effect on FEV1 than salbutamol although both were superior to IB. Only the first four subjects had two doses as originally intended, because the second administration of fenoterol resulted in marked cardiovascular effects and hypokalaemia. The observed differences in extrapulmonary effects between fenoterol and salbutamol provide a plausible group of mechanisms which may explain the increased risk of death associated with fenoterol in severe asthmatics.

Beta 2 adrenergic receptors in asthma: a current perspective

The role of the beta 2-adrenergic receptor in both the pathogenesis and treatment of asthma has been a subject of intense speculation and investigation for 25 years. The physiological effects of endogenous circulating catecholamines and exogenous adrenergic agonists in the lung are mediated by the beta 2-adrenergic receptor, which is present on a variety of cell types. Documented effects of beta 2-adrenergic receptor activation in the human lung include smooth muscle relaxation, inhibition of acetylcholine release from cholinergic nerve terminals, stimulation of serous and mucous cell secretion, increases in ciliary beat frequency, promotion of water movement into the airway lumen by stimulation of ion secretion across the apical membrane of epithelial cells, increase in bronchial blood flow, reduction in venular permeability, and inhibition of mediator release from some, but not all, inflammatory cells. Beta 2-Adrenergic receptors are present in normal or increased numbers on asthmatic airway smooth muscle but are uncoupled in severe asthma, leading to functional hyporesponsiveness, probably due to the effects of inflammatory mediators. There is also evidence for dysfunction of beta 2-adrenergic receptors on circulating inflammatory cells following mediator release. However, dysfunction of the receptors on airway smooth muscle and inflammatory cells is unlikely to be of primary importance in the pathogenesis of asthma. There is increasing concern that regular beta 2-adrenergic receptor agonist use in the therapy of asthma is deleterious. Although a number of theories have been advanced to explain such an effect, none is well established and further research is urgently required.