ADMINISTRATION ROUTES:
IV
ALTERNATIVE NAMES:
Proveblue
ICU INDICATIONS:
-
Methaemoglobinaemia
-
Vasoplegic shock (particularly after cardiopulmonary bypass)
PRESENTATION AND ADMINISTRATION:
IV:
0.5% Methylene blue (50 mg /10 mL) in 10 mL vial
Administer intravenously, undiluted, over a period of several minutes. Store at room temperature
Do not dilute with normal saline as this can cause precipitation
DOSAGE:
IV:
Give 1 - 2 mg/kg undiluted slow push (0.2 - 0.4 mL/kg of 0.5% solution)
May give subsequent dose if required
Do not exceed total of 7 mg/kg
DOSAGE IN RENAL FAILURE AND RENAL REPLACEMENT THERAPY:
No specific data available. Excreted via urine as leucomethylene blue. Contraindicated in severe renal impairment. Use with caution in mild to moderate renal impairment.
DOSAGE IN PAEDIATRICS:
IV:
1 mg/kg as single dose
May give subsequent dose if required
CLINICAL PHARMACOLOGY:
Methylene blue is 3, 7-bis(Dimethylamino)-phenothiazin-5-ium chloride. It will produce two opposite actions on haemoglobin. Low concentrations will convert methaemoglobin to haemoglobin. High concentrations convert the ferrous iron of reduced haemoglobin to ferric iron which results in the formation of methaemoglobin. Methylene blue is thought to reduce vasoplegia through actions involving nitric oxide.
CONTRAINDICATIONS:
- Known hypersensitivity to methylene blue
- Patients with Glucose-6-phosphate dehydrogenase deficiency
- Severe renal impairment
- Methaemoglobinaemia due to cyanide poisoning
- Patient also receiving monamine oxidase inhibitors (e.g. selegiline, moclobemide)
WARNINGS:
Spurious reduction in oximetry
Administration of methylene blue will cause any measurement of oximetry (pulse or continuous mixed venous) to incorrectly report hypoxaemia. Methylene blue has an absorption peak of 668 nm so absorbs most of the 660 nm oximeter light emission. The oximeter reports this as the presence of reduced haemoglobin, so reports a decrease in oxygen saturation. Pulse oximetry may report readings in the 70-80% range within a few seconds of injection; this may last for 15-30 minutes.
PRECAUTIONS:
General:
Do not exceed total dose of 7 mg/kg as this may paradoxically cause methaemoglobinaemia
Laboratory Tests:
No tests in addition to routine ICU tests are required
Drug/Laboratory Test Interactions:
None noted
IMPORTANT DRUG INTERACTIONS IN ICU:
None of note
ADVERSE REACTIONS:
Body as a Whole:
Dizziness, headache, confusion, methaemoglobinaemia
Gastrointestinal effects:
Abdominal pain