Adverse reactions to N-acetylcysteine.

Clinical details of seven patients who suffered adverse reactions to N-acetylcysteine as Parvolex are documented. Skin testing was carried out to diluted Parvolex, and its individual components N-acetylcysteine and ethylenediaminetetra-acetate, in five reacting patients and five patients who had received Parvolex with no ill-effects. Weal responses to high concentrations (20 mg/ml) of acetylcysteine as Parvolex were significantly greater (p less than 0.02) in reactors. There were no other significant differences between the groups. In two patients who reacted, the effects of intradermal Parvolex could be inhibited by prior therapy with the antihistamine terfenadine. These results suggest a 'pseudo-allergic' rather than an immunological aetiology for adverse reactions to Parvolex.