methylthioninium chloride: clinical use

Prescribing considerations

• Confirm acquired methaemoglobinaemia and its likely cause; co-oximetry is preferred because pulse oximetry may be misleading.
• Review recent serotonergic medicines and balance the urgent indication against serotonin-toxicity risk.
• Use particular caution in renal impairment, newborns and young infants, and aniline- or dapsone-associated cases.

Contraindications and cautions

• Hypersensitivity to methylthioninium chloride or other thiazine dyes
• G6PD deficiency
• NADPH reductase deficiency
• Nitrite-induced methaemoglobinaemia during cyanide-poisoning treatment
• Chlorate-induced methaemoglobinaemia

Monitoring

• Methaemoglobin concentration and clinical oxygenation, preferably using co-oximetry
• ECG and blood pressure during and after administration
• Evidence of haemolysis or hyperbilirubinaemia
• Features of serotonin syndrome
• Injection site and possible photosensitivity

Clinical pharmacology

An antidote that accelerates reduction of methaemoglobin to oxygen-carrying haemoglobin through an NADPH-dependent red-cell pathway. It is also a potent reversible monoamine oxidase inhibitor.

Formulation and product differences

• Clear dark-blue, single-use intravenous solution supplied in glass ampoules.
• May be diluted with glucose solution; sodium chloride solution is incompatible.
• Do not use cloudy, turbid, discoloured or particle-containing solution.

Injection

Route: Parenteral

Strengths: 5 mg/mL