No black box warning on record for Methylene Blue

As of the latest FDA labeling reviewed, Methylene Blue (methylene blue) does not carry a black box warning. Standard warnings and precautions still apply — see the full Methylene Blue medicine page for the complete safety profile.

Other warnings & precautions

SEROTONIN SYNDROME RISK: Methylene blue is a potent, reversible inhibitor of MAO-A. Concurrent use with serotonergic drugs including SSRIs, SNRIs, tricyclic antidepressants, tramadol, triptans, linezolid, and meperidine can cause severe or fatal serotonin syndrome. The FDA issued a Drug Safety Communication in 2011 warning against this combination. Avoid elective use if patient is on serotonergic agents; for urgent/emergency use, weigh risk-benefit carefully and monitor continuously.
G6PD DEFICIENCY CONTRAINDICATION: Patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency are unable to generate NADPH adequately, which is required for methylene blue to work. Not only will the drug fail to treat methemoglobinemia, it may cause severe, life-threatening hemolytic anemia. Screen for G6PD deficiency when clinically feasible; use alternative treatments (ascorbic acid, exchange transfusion) in confirmed deficiency.
PARADOXICAL METHEMOGLOBINEMIA AT HIGH DOSES: At cumulative doses exceeding 7 mg/kg, methylene blue itself acts as an oxidant and can paradoxically worsen methemoglobinemia. Adhere strictly to maximum dosing recommendations and re-evaluate if clinical response is inadequate at standard doses.
NEONATAL USE CAUTION: Neonates and infants under 3 months have immature NADPH-methemoglobin reductase enzyme systems. Methylene blue may be less effective and paradoxical methemoglobinemia is more likely. Consider exchange transfusion as first-line in severe neonatal methemoglobinemia.
PREGNANCY RISK: Intra-amniotic administration of methylene blue during amniocentesis has been associated with fetal intestinal atresia, hemolytic anemia, and death — this use has been abandoned. Systemic therapeutic use during pregnancy should only occur when the benefit clearly outweighs fetal risk; animal data and limited human data suggest potential harm.
SKIN AND TISSUE STAINING: Methylene blue irreversibly stains skin, mucous membranes, medical equipment, and clothing blue-green. Patients and healthcare providers should be counseled. Extravasation during IV administration can cause significant local tissue necrosis and staining.
RENAL IMPAIRMENT: Methylene blue and its metabolites (azure A, azure B) are primarily renally excreted. Accumulation may occur in significant renal impairment, potentially increasing the risk of adverse effects including serotonergic toxicity. Use with caution and monitor closely in patients with severe renal impairment (CrCl <30 mL/min).
HEMOLYTIC ANEMIA: Even in patients without G6PD deficiency, high doses or prolonged use can cause hemolytic anemia due to oxidative stress on red blood cells. Monitor CBC and signs of hemolysis (falling hemoglobin, elevated LDH, jaundice, dark urine) in patients receiving multiple doses or continuous infusions.
RAPID IV INJECTION HAZARD: Rapid IV bolus administration can cause severe, transient hypotension, cardiac arrhythmias, and intense local pain. Always administer IV methylene blue slowly over a minimum of 5 minutes, preferably into a large vein with adequate dilution.
DRUG INTERFERENCE WITH PULSE OXIMETRY: Methylene blue absorbs light at 660 nm (the wavelength used by pulse oximetry to detect oxyhemoglobin) and can cause falsely low SpO2 readings. Clinicians should not rely solely on pulse oximetry when methylene blue is administered; co-oximetry (blood gas with co-oximeter) is required for accurate methemoglobin measurement.

Other warnings & precautions

SEROTONIN SYNDROME RISK: Methylene blue is a potent, reversible inhibitor of MAO-A. Concurrent use with serotonergic drugs including SSRIs, SNRIs, tricyclic antidepressants, tramadol, triptans, linezolid, and meperidine can cause severe or fatal serotonin syndrome. The FDA issued a Drug Safety Communication in 2011 warning against this combination. Avoid elective use if patient is on serotonergic agents; for urgent/emergency use, weigh risk-benefit carefully and monitor continuously.

G6PD DEFICIENCY CONTRAINDICATION: Patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency are unable to generate NADPH adequately, which is required for methylene blue to work. Not only will the drug fail to treat methemoglobinemia, it may cause severe, life-threatening hemolytic anemia. Screen for G6PD deficiency when clinically feasible; use alternative treatments (ascorbic acid, exchange transfusion) in confirmed deficiency.

PARADOXICAL METHEMOGLOBINEMIA AT HIGH DOSES: At cumulative doses exceeding 7 mg/kg, methylene blue itself acts as an oxidant and can paradoxically worsen methemoglobinemia. Adhere strictly to maximum dosing recommendations and re-evaluate if clinical response is inadequate at standard doses.

NEONATAL USE CAUTION: Neonates and infants under 3 months have immature NADPH-methemoglobin reductase enzyme systems. Methylene blue may be less effective and paradoxical methemoglobinemia is more likely. Consider exchange transfusion as first-line in severe neonatal methemoglobinemia.

PREGNANCY RISK: Intra-amniotic administration of methylene blue during amniocentesis has been associated with fetal intestinal atresia, hemolytic anemia, and death — this use has been abandoned. Systemic therapeutic use during pregnancy should only occur when the benefit clearly outweighs fetal risk; animal data and limited human data suggest potential harm.

SKIN AND TISSUE STAINING: Methylene blue irreversibly stains skin, mucous membranes, medical equipment, and clothing blue-green. Patients and healthcare providers should be counseled. Extravasation during IV administration can cause significant local tissue necrosis and staining.

RENAL IMPAIRMENT: Methylene blue and its metabolites (azure A, azure B) are primarily renally excreted. Accumulation may occur in significant renal impairment, potentially increasing the risk of adverse effects including serotonergic toxicity. Use with caution and monitor closely in patients with severe renal impairment (CrCl <30 mL/min).

HEMOLYTIC ANEMIA: Even in patients without G6PD deficiency, high doses or prolonged use can cause hemolytic anemia due to oxidative stress on red blood cells. Monitor CBC and signs of hemolysis (falling hemoglobin, elevated LDH, jaundice, dark urine) in patients receiving multiple doses or continuous infusions.

RAPID IV INJECTION HAZARD: Rapid IV bolus administration can cause severe, transient hypotension, cardiac arrhythmias, and intense local pain. Always administer IV methylene blue slowly over a minimum of 5 minutes, preferably into a large vein with adequate dilution.

DRUG INTERFERENCE WITH PULSE OXIMETRY: Methylene blue absorbs light at 660 nm (the wavelength used by pulse oximetry to detect oxyhemoglobin) and can cause falsely low SpO2 readings. Clinicians should not rely solely on pulse oximetry when methylene blue is administered; co-oximetry (blood gas with co-oximeter) is required for accurate methemoglobin measurement.

Methylene Blue Black Box Warning

No black box warning on record for Methylene Blue

Other warnings & precautions

Methylene Blue Black Box Warning

No black box warning on record for Methylene Blue

Other warnings & precautions