Methylene blue is a very effective reducer of drug-induced methemoglobinemia. It has dose-dependent oxidation or reduction properties. In most cases, a dose of 1 to 2 mg/kg IV given over 5 minutes and immediately followed by a 15- to 30-mL fluid flush to minimize the local pain is both effective and relatively safe. The onset of action is quite rapid, and the effects are usually seen within 30 minutes. The dose may be repeated after 30 to 60 minutes and then every 2 to 4 hours as needed. The total dose should not exceed 7 mg/kg as a single dose or 15 mg/kg within 24 hours. Repeated treatment may be needed for treating compounds that have prolonged elimination or those compounds that undergo enterohepatic recirculation (e.g., dapsone). Methylene blue can cause dose-related toxicity. At high doses, methylene blue can also induce an acute hemolytic anemia and rebound methemoglobinemia. The reasons for treatment failure with methylene blue include ineffective GI decontamination, the existence of other forms of hemoglobin (e.g., sulfhemoglobin), a low or high dose of methylene blue and the toxicokinetics of some agents, such as aniline, benzocaine or dapsone.