Fomepizole

PUT THE CHILL ON ANTIFREEZE POISONING WITH THIS ANTIDOTE.

Fomepizole (Antizol) is an antidote to ethylene glycol poisoning that's less likely to cause central nervous system (CNS) depression than ethanol, the traditional antidote. Fomepizole also doesn't affect mental status or cause hypoglycemia, and therapeutic plasma concentrations are easier to maintain than with ethanol.

Ethanol has never officially been approved as an antidote for ethylene glycol poisoning, but its availability, low cost, and effectiveness have made it the first-line treatment worldwide. However, it can exacerbate circulatory problems, cause respiratory arrest, and cause CNS excitement that complicates nursing care. And because ethanol's kinetics are unpredictable, blood concentrations must be measured frequently.

Fomepizole, also known as 4-methylpyrazole, is the first drug approved as an antidote for ethylene glycol, the main component of antifreeze and coolants. About 5,000 cases of ethylene glycol poisoning are reported annually in the United States; ingestion is usually by mistake, as an attempt at suicide, or as a cheap substitute for alcohol.

Ethylene glycol poisoning should be suspected in cases of metabolic acidosis of otherwise unknown origin, and of toxin-induced renal failure.

Mechanism of action: Fomepizole inhibits alcohol dehydrogenase, the substance that catalyzes ethylene glycol into toxic metabolites including glycolic acid and oxalic acid. (Ethylene glycol itself isn't toxic.)

Indications: Use fomepizole as an antidote for ethylene glycol poisoning or to treat suspected ethylene glycol ingestion.

Dosage (adults): Withdraw the appropriate dose from the vial and inject it into at least 100 ml of 0.9% sodium chloride solution or 5% dextrose injection. Administer it as a slow intravenous infusion over 30 minutes.

Give a loading dose of 15 mg/kg, followed by doses of 10 mg/kg every 12 hours for four doses, and then 15 mg/kg every 12 hours until ethylene glycol blood concentrations have been reduced below 20 mg/dl. Fomepizole'ssafety and efficacy in children haven't been established.

Adverse reactions: headache, nausea, dizziness, rash, and other allergic reactions (rare) Contraindications and precautions: Don't give fomepizole to patients known to be hypersensitive to the drug or to other pyrazoles.

Nursing considerations:

Fomepizole, a liquid, is supplied in vials containing 1.5 grams of the drug ( 1 gram/ml). Its melting point is 77 deg F (25 deg C), however, so it may be in solid form at room temperature. If the drug has solidified in the vial, liquefy it by running the vial under warm water or by holding it in your hand. Solidification doesn't affect the drug's efficacy, safety, or stability.

Fomepizole may irritate the vein, so don't administer it as a bolus injection or give it undiluted.

Assess the patient for possible metabolic acidosis, acute renal failure, acute respiratory distress syndrome, and hypocalcemia.

Prepare the patient for possible dialysis if he has renal failure, significant or worsening metabolic acidosis, or a measured ethylene glycol concentration of more than 50 mg/dl. Consult the product labeling for dosage recommendations for patients requiring hemodialysis.

Because fomepizole is excreted by the kidneys, the risk of toxic reactions may be greater in patients with impaired renal function and in elderly patients.

Fomepizole's effects on the fetus aren't known. Administer this drug to pregnant women only if it's clearly needed.

Use caution when administering fomepizole to nursing mothers because researchers don't know if the drug is excreted in breast milk.

Copyright Springhouse Corporation Apr 2000
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