No influence of acetylcysteine on gas exchange and spirometry in chronic asthma

Non-smoking patients (n:25) with stable symptomatic asthma were investigated with regard to the pulmonary effects of N-acetylcysteine (NAC), peroral dose 200 mg three times daily, in a crossover double-blind study. They were studied once a week for 9 weeks, with a run-in period and periods with NAC and placebo (3 weeks each). Functional residual capacity and specific airway resistance were 19 and 53% larger, respectively, and forced expiratory variables (FEV%, MEF25) were 20 and 53% lower than reference values. Distribution of ventilation-perfusion ratios (VA/Q), assessed by multiple inert gas elimination technique with peripheral venous sampling, was abnormal, although arterial PO2 and PCO2 were within normal limits. NAC medication had no effect on any spirometric, lung mechanic or gas exchange variable, nor on the frequency of pulmonary symptoms.