Our hypothesis is that while an increase in histamine may be observed in response to NAC, no change in the other mediators commonly associated with anaphylactic reactions will be demonstrated. Blood samples will be obtained at baseline, at the end of the study, and at 10-min intervals during the incremental dose infusion of NAC to include each of the 6 doses administered (total 14 occasions). To maximise efficiency in addressing our hypothesis we intend to measure histamine and NAC at each time point. Enough blood will also be drawn on each occasion for measurement of other potential inflammatory mediators, including tryptase, vWF, tPA, IL-6, PGD2, and PGI2.