- heterocyclic aromatic molecule
MECHANISM OF ACTION
- two opposite actions on Hb
(1) low concentrations: methylene blue -> NADPH-dependent reduction to leucomethylene blue (due to action of methaemoglobin reductase) -> reduces methaemoglobin -> Hb
(2) high concentrations: methylene blue -> converts ferrous iron of reduced Hb to ferric ion -> forms methaemoglobin
- inhibits guanylate cyclase (which is stimulated by NO and other mediators), thus decreasing C-GMP and vascular smooth muscle relaxation
- MAO inhibition
- stored at room temperature
- 1-2mg/kg IV over 5 minutes followed by saline flush; repeat at 30-60 min if MetHb levels not falling
- repeat dose every 6-8h when MetHb continues for days, e.g. dapsone toxicity
- 1.5-2 mg/kg IV over 30-60min
— asymptomatic with >20% MetHb, or >10% if risk factors such as anaemia or ischemic heart disease
- vasoplegic shock post cardiopulmonary bypass
- other possible roles in critical illness: hepatopulmonary syndrome, septic shock
- other uses have included use as an antimalarial agent, anti-cancer treatment, treatment of ifosfamide neurotoxicity, as a dye/stain (e.g. test for aspiration), priapism
- G6PD deficiency (lack of NADPH prevents methylene blue from working and may lead to haemolysis)
- renal impairment
- methaemoglobin reductase deficiency
- nitrite-induced methaemoglobinaemia due to cyanide poisoning
- inability to monitor oxygen saturation by SpO2 or continuous central venous saturation monitoring
- non-specific symptoms: dizziness, headache, confusion, chest pain, shortness of breath, nausea and vomitng
- local pain and irritation
- blue staining of mucous membrane may mimic cyanosis
- paradoxical methaemoglobinaemia due to direct oxidative effect on Hb (typically at very high doses > 7 mg/kg)
- acute haemolytic anemia in G6PD deficiency (typically doses >15mg/kg)
- MAO inhibiton may contribute to serotonin toxicity or hypertensive crisis
- Absorption – given IV
- Distribution – ?
- Metabolism – rapidly converted to leucomethylene blue by methemoglobin reductase
- Elimination – leucomethylene is mostly excreted in the urine as a salt complex
Levin, R.L., et al (2004) “Methylene Blue Reduces Mortality and Morbidity in Vasoplegic Patients After Cardiac Surgery” Ann Thorac Surg 77:496-9 PMID: 14759425.
- NO is a mediator involved in post cardiac surgery vasoplegia (SIRS)
- methylene blue (2mg/kg) vs placebo
- vasoplegia defined as: hypotension, MAP <50mmHg, low filling pressures, CVP <5, normal or elevated cardiac index of > 2.5L/min/m2, low peripheral resistance dramatic resolution of vasoplegia!
- vasoplegic postoperative syndrome was seen in 8.8% of all patients (636 total)
-> better outcomes in every area of study!
-> morbidity and mortality reductions (0% versus 21.4% or 6 of 28 patients; p value = 0.01)
References and Links
- Ginimuge PR, Jyothi SD. Methylene blue: revisited. J Anaesthesiol Clin Pharmacol. 2010 Oct;26(4):517-20. PubMed PMID: 21547182; PubMed Central PMCID: PMC3087269.
- Levin RL, Degrange MA, Bruno GF, Del Mazo CD, Taborda DJ, Griotti JJ, Boullon FJ. Methylene blue reduces mortality and morbidity in vasoplegic patients after cardiac surgery. Ann Thorac Surg. 2004 Feb;77(2):496-9. PMID: 14759425.
Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.
After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.
He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE. He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.
His one great achievement is being the father of three amazing children.
On Twitter, he is @precordialthump.