METHYLENE BLUE
Clinical safety rating: caution
Comprehensive clinical and safety monograph for METHYLENE BLUE (METHYLENE BLUE).
Methylene blue is a dye that acts as a redox agent, reducing methemoglobin to hemoglobin by activating the enzyme methemoglobin reductase. It also inhibits nitric oxide synthase and guanylate cyclase, causing vasoconstriction in septic shock.
| Metabolism | Reduced to leukomethylene blue by NADPH-dependent reductases (e.g., methemoglobin reductase) and other flavin reductases; subsequently metabolized by glucuronidation or sulfation in the liver; partially excreted unchanged in urine. |
| Excretion | Renal (80% as leukomethylene blue and unchanged drug); biliary/fecal minor |
| Half-life | Terminal elimination half-life approximately 12–24 hours; clinically, levels may persist for 2–3 days due to enterohepatic recycling |
| Protein binding | Approximately 50% bound to plasma proteins (albumin and others) |
| Volume of Distribution | 0.7–1.2 L/kg; indicates extensive extravascular distribution including RBCs and tissues |
| Bioavailability | Oral: 53–73% (first-pass metabolism to leuko form); IV: 100% |
| Onset of Action | Oral: 30–60 minutes; Intravenous: seconds to minutes; Intramuscular: 15–30 minutes |
| Duration of Action | Methemoglobin reduction: 2–6 hours after single IV dose; optical staining effects may last 4–7 days; enterohepatic recycling may prolong effects |
| Molecular Weight | 319.85 |
1-2 mg/kg IV over 5-30 minutes for methemoglobinemia; repeat after 1 hour if needed. Maximum dose: 7 mg/kg.
| Dosage form | SOLUTION |
| Renal impairment | No specific GFR-based adjustment required; use with caution in severe impairment (eGFR <30 mL/min/1.73m²) due to potential accumulation. |
| Liver impairment | Child-Pugh A: no adjustment; Child-Pugh B or C: reduce dose by 50% or consider alternative due to risk of serotonin syndrome (drug affecting hepatic metabolism). |
| Pediatric use | 1-2 mg/kg IV (maximum dose 7 mg/kg) for methemoglobinemia; repeat after 1 hour if necessary. Preferred concentration 1% solution. |
| Geriatric use | No specific dose adjustment; monitor for serotonin syndrome and renal function (age-related decreased clearance). Start at lower end of dosing range. |
| 1st trimester | Not recommended due to potential teratogenicity (case reports of hemolytic anemia and hyperbilirubinemia). Use only if clearly needed. |
| 2nd trimester | Limited data; use with caution. May cause fetal methemoglobinemia and hemolytic anemia in G6PD deficiency. |
| 3rd trimester | Avoid near term due to risk of neonatal hemolytic anemia and hyperbilirubinemia. |
Clinical note
Comprehensive clinical and safety monograph for METHYLENE BLUE (METHYLENE BLUE).
| Placental transfer | Crosses placenta; evidence from in vitro and animal studies. |
| Breastfeeding | Excreted into breast milk; avoid use in breastfeeding due to potential for infant toxicity (hemolysis, methemoglobinemia). |
| Lactation Rating |
■ FDA Black Box Warning
Serotonin syndrome: Methylene blue inhibits monoamine oxidase A (MAO-A), increasing serotonin levels. Life-threatening serotonin syndrome can occur when combined with serotonergic drugs (e.g., SSRIs, SNRIs, MAOIs). Avoid use in patients taking serotonergic agents, or discontinue serotonergic drugs at least 5 weeks before methylene blue administration.
| Serious Effects |
G6PD deficiencySevere renal impairmentHypersensitivity to methylene blueUse with SSRIs, SNRIs, or MAOIs (risk of serotonin syndrome)Pregnancy (except for emergency indications)
| Precautions | Risk of serotonin syndrome with serotonergic drugs; avoid concurrent use or discontinue serotonergic agents 5 weeks prior., Hemolytic anemia in G6PD deficiency (may cause Heinz body formation)., Hypersensitivity reactions (rash, urticaria, anaphylaxis)., Interference with pulse oximetry readings (may cause falsely low SpO2). |
| Food/Dietary | No specific food interactions have been reported. However, patients should avoid tyramine-rich foods if taking concomitant MAOIs due to potential hypertensive crisis, though methylene blue is a weak MAOI. St. John's wort may increase serotonin syndrome risk. Avoid alcohol and caffeine in excess as they may exacerbate side effects. |
Loading safety data…
| L5 (Contraindicated) |
| Teratogenic Risk | Methylene blue is contraindicated in the first trimester due to risk of fetal harm, including methemoglobinemia and hemolytic anemia. In second and third trimesters, use only if clearly needed; may cause fetal methemoglobinemia and hyperbilirubinemia. |
| Fetal Monitoring | Monitor maternal and fetal heart rate, methemoglobin levels (if high-dose or prolonged use), and signs of hemolysis in mother and fetus. Assess umbilical cord blood gases if used during labor. |
| Fertility Effects | No specific data on human fertility impairment. Animal studies show no adverse effects on fertility at therapeutic doses. |
| Clinical Pearls | Methylene blue is a first-line antidote for methemoglobinemia (dose: 1-2 mg/kg IV over 5 minutes; may repeat in 1 hour). It is contraindicated in G6PD deficiency due to risk of hemolytic anemia. Serotonin syndrome risk when combined with serotonergic drugs (e.g., SSRIs, MAOIs); avoid use in patients taking such agents. Monitor for blue-green discoloration of urine, skin, and sclera. Use with caution in renal impairment; not dialyzable. |
| Patient Advice | You may notice blue-green discoloration of your urine, skin, and eyes; this is harmless and will fade after treatment. · Avoid taking certain antidepressants (e.g., SSRIs, MAOIs) while receiving methylene blue due to risk of serious serotonin syndrome. · If you have glucose-6-phosphate dehydrogenase (G6PD) deficiency, inform your doctor immediately as this drug can cause red blood cell breakdown. · This medication may interfere with pulse oximetry readings, giving falsely low oxygen saturation levels. · Tell your healthcare provider if you are pregnant, breastfeeding, or plan to become pregnant. |