The effect of pyridostigmine on respiratory function in healthy and asthmatic volunteers

Respiratory function was evaluated in 12 healthy and 13 asthmatic volunteers following a single oral dose of pyridostigmine in a double-blind, placebo-controlled cross-over study. Respiratory function tests were performed at rest and after submaximal exercise at the time corresponding to the expected peak cholinesterase inhibition by pyridostigmine. A single dose of 60 mg pyridostigmine given to nonasthmatic subjects led to a decrease of 28.4% in cholinesterase activity when compared to the baseline and a statistically (but not physiologically) significant decrease in FEV₁ (forced expiratory volume in 1 sec) both at rest (P<0.015) and after exercise (P<0.05). This effect showed a strong correlation to the degree of cholinesterase inhibition (r = -0.936, P<0.0001). According to these findings, a smaller dose of pyridostigmine (30 mg) was given to subjects with mild bronchial asthma. At that dose, pyridostigmine resulted in a similar inhibition of cholinesterase activity to a mean of 76.7% of the baseline. A significant decrease in the pulse rate was also found (P<0.005). However, no changes in respiratory function were observed when compared with the effects of placebo. The effect of post-exertion atropine inhalation on respiratory function was also unchanged with pyridostigmine at that dose. We conclude that, in general, at this dose pyridostigmine is a safe drug for asthmatics; however, the distribution of individual results in this group cannot preclude the existence of a subpopulation of asthmatic patients who are more vulnerable to the effects of pyridostigmine.