Methylene Blue

ADMINISTRATION ROUTES:

IV

ALTERNATIVE NAMES:

Proveblue

ICU INDICATIONS:

1. Methaemoglobinaemia

2. 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:

1. Known hypersensitivity to methylene blue
2. Patients with Glucose-6-phosphate dehydrogenase deficiency
3. Severe renal impairment
4. Methaemoglobinaemia due to cyanide poisoning
5. 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