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Poisoning Information for the Public & Health Care Professionals
Last updated: 12/2017


Antizol®, 4-methylpyrazole, 4-MP

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Antizol®, 4-methylpyrazole, 4-MP


  • Suspected or confirmed ethylene glycol or methanol poisoning.
  • Exposure to other substances metabolized by alcohol dehydrogenase (diethylene glycol, glycol ethers).
  • Adjunctive treatment for massive acetaminophen overdoses; requires consultation with the poison centre.


  • Initial dose: 15 mg/kg IV over 30 minutes.
  • Maintenance Doses (No hemodialysis): 12 hours after the initial dose, administer 10 mg/kg IV over 30 minutes every 12 hours for 4 doses if needed.  Additional doses require an increase to 15 mg/kg IV every 12 hours.  Continue until criteria for discontinuation are met: normal acid-base status, ethylene glycol level less than 3 mmol/L or methanol level less than 6 mmol/L.  All doses to be infused over 30 minutes.
  • Maintenance Doses (During hemodialysis): Same as above but dosing frequency increases to q4h. See table below for timing of doses.

Time in Relation to Hemodialysis

Time Since Last Dose of Fomepizole

Fomepizole Dosing

Before dialysis

Greater than 6 hours

Administer the next dose.

During dialysis


Administer doses every 4 hours.

Post dialysis

Less than 1 hour

Give the next dose 12 hours after the last dose administered, and then follow the normal dosing schedule.

Post dialysis

Greater than or equal to 1 hour but less than 3 hours

Immediately administer 50% of the next scheduled dose, and then follow the normal dosing schedule.

Post dialysis

Greater than or equal to 3 hours

Immediately administer 100% of the next dose, and then follow the normal dosing schedule.


  • Infusion: Dilute each dose in 100 mL of sodium chloride 0.9% or dextrose 5% in water and administer over 30 minutes.
  • Fomepizole should NOT be administered undiluted or direct.
  • When preparing fomepizole, avoid ocular, dermal or inhalational exposure. In case of eye or skin exposure, flush immediately with copious amounts of water. Prepare in well-ventilated area.

Compatibility, Stability

  • Compatible with sodium chloride 0.9% and dextrose 5% in water.
  • Fomepizole solidifies at temperatures less than 25º C. If the solution becomes solid in the vial, it should be liquefied by running the vial under warm water or by holding it in the hand. Solidification does not affect the stability of the product.

Potential Hazards of Administration

  • Headache, nausea.
  • Dizziness, increased drowsiness.
  • Bad or metallic taste.
  • Minor allergic reactions (rash, eosinophilia).


  • Fomepizole inhibits the metabolism of ethanol, and vice versa.

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