Methaemoglobinaemia

MEDICINES INFORMATION FREQUENTLY ASKED QUESTION

Methylthioninium chloride (Methylene Blue) injection administration before parathyroid surgery

Question:

How to administer methylthioninium chloride (Methylene Blue) injection before parathyroid surgery.  This is used prior to surgery to stain the parathyroid glands.

NOTE: this is an off-label (unlicensed) use of methylthioninium chloride. Evaluate safety carefully in light of the potential for CNS toxicity, (see safety warning above).

Methylthioninium chloride (Methylene Blue) 0.5% injection is kept in stock. It is available as 10ml ampoules (i.e. 50mg amps).

Answer:

The patient must be weighed on admission.

The dose to be administered is calculated as 3mg/Kg.

The calculated dose must be diluted with glucose 5%.

The volume of the infusion depends on the dose - maximum recommended concentration is 350mg in 500ml - higher concentrations result in an increased risk of thrombophlebitis.

Dose                                      Infused volume

Up to 350mg                      500mls

351mg - 420mg                  600mls

421mg - 490mg                  700mls

491mg - 560mg                  800mls

Each 10ml ampoule contains 50mg of methylene blue.

Infuse over 45 - 60 minutes prior to surgery. Preferably methylthioninium chloride should be given via a central line as extravasation may cause tissue damage. Prepare immediately before use and administer through a sterile 0.45 micron filter.

Limitations: Applies to adult patients with normal renal function.

Methylthioninium chloride (methylene blue) in high intravenous doses should be avoided in patients taking serotonergic drugs eg SSRIs, clomipramine, mirtazepine, venlafaxine. CNS toxicity has been reported following administration of methylene blue to patients taking serotonergic drugs.

For more detail on reported cases and advice on prescribing see Drug Safety Update December 2014

Prepared by Medicines Information 2006  updated 2019