Fomepizole Intravenous for Adults

Who can administer

May be administered by registered competent doctor or nurse/midwife

Important information

• Doses specified in this monograph are based on the Toxbase database, and differ from manufacturer's advice
• Poisons Centre must be contacted prior to using this drug
• See monitoring requirements - next page
• Unlicensed preparation
• Very limited stock in GUH - contact pharmacy immediately if a patient is commenced on fomepizole so that further supplies can be organised - see emergency supply contact numbers
• Available in Emergency Department - antidote press in Resus room

Available preparations

Antizol 1.5g per 1.5mL vial

Fomepizole 1.5g per 1.5mL (SteriMax)

Reconstitution

Already in solution

• The drug solidifies at temperatures less than 25⁰C. If the drug solution has become solid, it should be liquefied by running the vial under warm water or by holding in the hand
• Solidification does not affect the safety, efficacy or stability of the drug

Dilute further prior to administration

Infusion fluids

Sodium chloride 0.9% or Glucose 5%

Methods of intravenous administration

Intermittent intravenous infusion (administer using an electronically controlled infusion device)

• Dilute dose with at least 100mL infusion fluid. (Toxbase suggests 250 to 500ml)
• Administer over 30 minutes

Dose in adults

IMPORTANT

• Doses specified in this monograph are based on the Toxbase database, and differ from manufacturer's advice
• For patients weighing more than 110kg the antidote dose should be calculated using a maximum of 110kg, rather than the patient's actual weight ^{(ref 1)}

Loading dose (for patients NOT on haemodialysis)

• Give 15mg/kg (to a max dose of 1650mg) over 30 minutes
• The loading dose is still needed in patients who have begun treatment with ethanol as an antidote, who are being switched to fomepizole treatment ^{(ref 1)}

Followed by:

• Doses of 10mg/kg (max dose of 1100mg) over 30 minutes, every twelve hours for four doses, (starting at 12 hours after the loading dose is given ^{(ref 1)})
• After these four doses then give 15mg/kg (max dose of 1650mg) over 30 minutes, every twelve hours thereafter until ethylene glycol or methanol levels are undetectable or have been reduced below 50mg/dL ^{(ref 1)} (below 20mg/dL according to manufacturer) AND acidosis and signs of systemic toxicity have resolved. Consult specialist centre for advice

Haemodialysis ^{(ref 1)}

Consult specialist centre for advice

• If RRT is initiated more than 6 hours after the last fomepizole dose, or if no fomepizole has been given, administer a loading dose of 15mg/kg (max 1,650mg) over 30 minutes. (another loading dose is not required if six or fewer hours have elapsed since the last dose)
• For the entire duration of RRT (including time between dialysis sessions) fomepizole may either be given as
  • infusion of 1mg/kg/hour
  • or
  • give 10mg/kg (max 1,100mg) every four hours
• At the end of RRT
  • if less than 1 hour has passed since the last dose was given, await four hours before restarting twelve-hourly dosing
  • if 1 to 3 hours has passed, give half the dose and restart twelve-hourly dosing in six hours;
  • if more than 3 hours has passed, administer the next twelve-hourly dose

Monitoring

• Monitor ethylene glycol or methanol concentrations in serum and urine, and the presence of urinary oxalate crystals
• Monitor LFTs, white blood counts during treatment as transient increases in serum transaminase levels and eosinophilia have been noted with repeated fomepizole dosing

Storage

• Store between 20 and 25⁰C
• See under reconstitution re temperature changes effects on product

References

Antizol;Package insert 2nd May 2017

Fomepizole (SteriMax) June 14th 2018

(1) Toxbase (accessed online 29/09/21)

Therapeutic classification

Antidote