Safety of N-Acetylcysteine at High Doses in Chronic Respiratory Diseases: A Review

N-Acetylcysteine (NAC) is widely used in respiratory medicine, with a maximum licensed dose in chronic use of 600 mg/day; however, some clinical trials have studied the efficacy of NAC at higher doses. The aim of this review was to evaluate the adverse effects profile of NAC at higher than the standard dose in chronic respiratory diseases to establish a risk–benefit ratio in increasing the daily dose; therefore, studies using NAC at a dose of at least 600 mg/day were selected. Forty-one articles where NAC has been used at 600 mg and above, up to 3000 mg/day, and with a specific report on safety, were considered. Most of the studies used oral NAC and were conducted on patients with chronic obstructive pulmonary disease, idiopathic pulmonary fibrosis, bronchiectasis, chronic bronchitis and cystic fibrosis. In general, the safety profile was similar at both the high and standard doses with the oral formulation; gastrointestinal symptoms were reported but they were no more common than in the control group.