Methylene blue - an emerging vasopressor

Table 2 Adverse effects[28-31]

Adverse effect	Comments/mechanism
Hemolysis (glucose-6-phosphate dehydrogenase deficiency)	Contraindicated; oxidative stress triggers hemolysis
Methemoglobinemia	< 2% incidence; dose-related
Serotonin syndrome	Occurs with MAOI/SSRI co-administration
Green-blue discoloration	Urine/secretions/skin; due to metabolites; affects pulse oximetry
Pulse oximetry artifacts	Spurious low SpO2; due to light absorption
Fall in P/F ratio	Possibly from pulmonary vasoconstriction → V/Q mismatch. Rare-high doses 31
Splanchnic vasoconstriction	At doses > 7 mg/kg (possibly > 4 mg/kg)
Extravasation injury	Can cause necrosis; central line preferred
ECG changes, diaphoresis, dyspnea	Reported at higher doses
Pregnancy risk	Avoid use; insufficient safety data

MAOI/SSRI: Monoamine oxidase inhibitor/selective serotonin reuptake inhibitor; P/F: PaO₂/FiO₂ ratio; V/Q: Ventilation/perfusion; ECG: Electrocardiogram.