Methylene Blue

Liverpool Hospital Emergency Department


Use as an antidote for methaemoglobulinaemia 

  • Levels of MetHb >20% even if asymptomatic
  • Evidence of tissue hypoxia
  • Use as a vasopressor agent in severe vasoplegic shock 


  • 1% methylene blue 50mg/5ml 

Dosage and Administration 

  • 1-2mg/kg as a slow IV push over 5 minutes followed by saline flush further dosing may be guided by a toxicologist.
  • Generally, a single dose is required except if there is ongoing oxidising and production of  MetHb.
  • Measure MetHb hourly post administration on blood gases 

Side Effects: 

  • Dysuria
  • Green blue urine 

Pit Falls:  

Failure of treatment can occur 

  • Inadequate dosage
  • Ongoing methhb production
  • Sulfhaemoglobin
  • G6PD deficiency
  • Abnormal Hb
  • Excessive methylene blue can cause methb (>7mg/kg)