Should anticholinergics be used in acute severe asthma?

Anticholinergic drugs have been used in Western medicine for the treatment of asthma since the early 19th century. Studies evaluating drug efficacy in acute severe asthma over the last decade have renewed interest in the optimal use of anticholinergics in this condition. Unlike other bronchodilators (i.e., beta 2-agonists and methylxanthines), the anticholinergics produce bronchodilation only by inhibiting cholinergic-mediated bronchospasm. Therefore, anticholinergic drugs are more dependent on the mechanism of bronchospasm than other bronchodilators. The 18 clinical trials of anticholinergics in acute severe asthma are critically reviewed for design and endpoint measurements. Anticholinergics alone produce a modest bronchodilation in acute severe asthma but are not as consistently effective as beta 2-agonists. Anticholinergics consistently produce an added bronchodilation to aerosolized beta 2-agonists in single- and multiple-dose studies. This bronchodilation appears to be greater in the more severely obstructed patients. This bronchodilation is generally modest (10-20 percent), has not yet been shown to produce greater overall outcome, and has not been evaluated against high-dose frequent administration of aerosolized beta 2-agonists. Currently, only the quaternary amine derivatives are recommended for use in acute asthma. These agents should be reserved as second-line agents for acute severe asthma except possibly for those patients presenting with more severe obstruction (peak expiratory flow rate less than 35 percent of predicted).