Pharmacologic studies of delirium prevention include trials comparing one sedative–analgesic regimen with another and studies of antipsychotic drugs administered with the specific intent of preventing delirium. Four placebo-controlled trials have evaluated pharmacologic prophylaxis of delirium; low-dose haloperidol48 and low-dose risperidone49 both reduced the incidence of delirium, as did a single low dose of ketamine during the induction of anesthesia.50 However, these trials were conducted among patients undergoing elective surgical procedures, and it is not clear whether their results can be extrapolated to the general ICU population. In contrast, the cholinesterase inhibitor rivastigmine was ineffective in preventing delirium.