Pharmacology. Acetylcysteine (N-acetylcysteine [NAC]) is a mucolytic agent that acts as a sulfhydryl group donor, substituting for the usual sulfhydryl donor of the liver, glutathione. It rapidly binds (detoxifies) the highly reactive electrophilic intermediates of metabolism, or it may enhance the reduction of the toxic intermediate, NAPQI, to the parent, acetaminophen. It is most effective in preventing acetaminophen-induced liver injury when given early in the course of intoxication (within 8 to 10 hours), but it may also be of benefit in reducing the severity of liver injury by several proposed mechanisms (improved blood flow and oxygen delivery, modified cytokine production, free radical or oxygen scavenging), even when given after 24 hours. This proposed role of NAC as a glutathione precursor, direct sulfhydryl binding agent, and antioxidant has also been the basis for its investigational use for poisonings from agents that are associated with a free radical or oxidative stress mechanism of toxicity or that bind to sulfhydryl groups. It may be used empirically when the severity of ingestion is unknown or serum concentrations of the ingested drug are not immediately available.