Reasons why a patient with methemoglobinemia may fail to respond to an infusion of methylene blue:
(1) ongoing exposure to a potent oxidizing chemical causing further methemoglobinemia
(2) methylene blue overdose
(3) G6PD deficiency
(4) NADPH methemoglobin reductase deficiency
(5) sulfhemoglobinemia
Differential diagnosis:
(1) The person does not have methemoglobinemia..
(2) Infusion of methylene blue may impart a bluish color to the skin that may be mistaken for methemoglobinemia. In this situation the patient is clinically improved.
(3) The methylene blue was given orally and not intravenously.
When faced with a person who is not responding to methylene blue therapy:
(1) re-evaluate the patient for possible sources of chemical or drug exposure that must be stopped
(2) exchange transfusion
(3) hyperbaric oxygen therapy (but can only be given for limited periods of time)
(4) large doses of ascorbic acid
