l INDICATIONS AND DOSE

Drug- or chemical-induced methaemoglobinaemia

 BY SLOW INTRAVENOUS INJECTION

 Child 3 months–17 years: Initially 1–2 mg/kg, then 1–2 mg/kg after 30–60 minutes if required, to be given over 5 minutes, seek advice from National Poisons Information Service if further repeat doses are required; maximum 7 mg/kg per course  Adult: Initially 1–2 mg/kg, then 1–2 mg/kg after 30–60 minutes if required, to be given over 5 minutes, seek advice from National Poisons Information Service if further repeat doses are required; maximum 7 mg/kg per course Aniline- or dapsone-induced methaemoglobinaemia

 BY SLOW INTRAVENOUS INJECTION

Child 3 months–17 years: Initially 1–2 mg/kg, then 1–2 mg/kg after 30–60 minutes if required, to be given over 5 minutes, seek advice from National Poisons Information Service if further repeat doses are required; maximum 4 mg/kg per course ? Adult: Initially 1–2 mg/kg, then 1–2 mg/kg after 30–60 minutes if required, to be given over 5 minutes, seek advice from National Poisons Information Service if further repeat doses are required; maximum 4 mg/kg per course

l CAUTIONS

Chlorate poisoning (reduces efficacy of methylthioninium).G6PD deficiency (seek advice from National Poisons Information Service). methaemoglobinaemia due to treatment of cyanide poisoning with sodium nitrite (seek advice from National Poisons Information Service). pulse oximetry may give false estimation of oxygen saturation

l INTERACTIONS → Appendix 1:

methylthioninium chloride

l SIDE-EFFECTS  

Common or very common Abdominal pain . anxiety . chest pain . dizziness . headache . hyperhidrosis . nausea . pain in extremity . paraesthesia . skin reactions .taste altered . urine discolouration . vomiting  Frequency not known Aphasia . arrhythmias . confusion . faeces discoloured . fever. haemolytic anaemia . hyperbilirubinaemia (in infants). hypertension . hypotension . injection site necrosis . mydriasis .tremor

l PREGNANCY No

information available, but risk to fetus of untreated methaemoglobinaemia likely to be significantly higher than risk of treatment.

l BREAST FEEDING

Manufacturer advises avoid breastfeeding for up to 6 days after administration—no information available.

l RENAL IMPAIRMENT

Dose adjustments Use with caution in severe impairment; dose reduction may be required.

l DIRECTIONS FOR ADMINISTRATION

 In children For intravenous injection, may be diluted with Glucose 5% to minimise injection-site pain; not compatible with Sodium Chloride 0.9%.