Dosage Forms
Excipient information presented when available (limited, particularly for generics); consult specific product labeling. [DSC] = Discontinued product
Solution, Intravenous [preservative free]:
Antizol: 1 g/mL (1.5 mL)
Generic: 1 g/mL (1.5 mL [DSC]); 1.5 g/1.5 mL (1.5 mL)
Pharmacology
Mechanism of Action
Fomepizole competitively inhibits alcohol dehydrogenase, an enzyme which catalyzes the metabolism of ethanol, ethylene glycol, and methanol to their toxic metabolites. Ethylene glycol is metabolized to glycoaldehyde, then oxidized to glycolate, glyoxylate, and oxalate. Glycolate and oxalate are responsible for metabolic acidosis and renal damage. Methanol is metabolized to formaldehyde, then oxidized to formic acid. Formic acid is responsible for metabolic acidosis and visual disturbances.
Pharmacokinetics/Pharmacodynamics
Absorption
Oral: Readily absorbed
Distribution
Vd: 0.6-1.02 L/kg; rapidly distributes into total body water
Metabolism
Hepatic to 4-carboxypyrazole (80% to 85% of dose), 4-hydroxymethylpyrazole, and their N-glucuronide conjugates; following multiple doses, induces its own metabolism via CYP oxidases after 30-40 hours
Excretion
Urine (1% to 3.5% as unchanged drug and metabolites)
Onset of Action
Peak effect: Maximum: 1.5-2 hours
Half-Life Elimination
Has not been calculated; varies with dose
Protein Binding
Negligible
Use: Labeled Indications
Ethylene glycol or methanol poisoning: Treatment of methanol or ethylene glycol poisoning alone or in combination with hemodialysis
Note: Fomepizole is the preferred antidote for known or suspected ethylene glycol poisoning or methanol poisoning. If fomepizole is unavailable or if the patient is intolerant to fomepizole, ethanol therapy may be considered. Ethanol as an antidote is effective in the management of methanol and ethylene glycol poisoning (Thanacoody 2016; Zakharov 2015); however, ethanol is associated with a higher incidence of adverse events and medication errors (Bestic 2009; Lepik 2009; Lepik 2011).
Contraindications
Hypersensitivity to fomepizole, other pyrazoles, or any component of the formulation
Dosage and Administration
Dosing: Adult
Note: Fomepizole therapy should begin immediately upon suspicion of ethylene glycol or methanol ingestion.
Ethylene glycol and methanol toxicity: IV: Loading dose of 15 mg/kg should be administered, followed by doses of 10 mg/kg every 12 hours for 4 doses, then 15 mg/kg every 12 hours thereafter until ethylene glycol or methanol concentrations have been reduced to <20 mg/dL and patient is asymptomatic with normal pH. Note: For severe toxicity requiring concomitant hemodialysis, see dosage adjustment in renal impairment.
Dosing: Geriatric
Specific studies have not been conducted in elderly patients.
Dosing: Pediatric
Note: Fomepizole therapy should begin immediately upon suspicion of ethylene glycol or methanol ingestion.
Ethylene glycol or methanol toxicity; patient not requiring hemodialysis: Limited data available; consider consultation with a clinical toxicology or poison control center: Infants, Children, and Adolescents: IV: Initial: 15 mg/kg loading dose; followed by 10 mg/kg every 12 hours for 4 doses; then 15 mg/kg every 12 hours until ethylene glycol or methanol concentrations have been reduced to <20 mg/dL and patient is asymptomatic with normal pH (Baum 2000; Benitez 2000; Boyer 2001; Brown 2001; De Brabander 2005; Detaille 2004; Fisher 1998). Note: For severe toxicity requiring concomitant hemodialysis, see Dosage adjustment in renal impairment.
Reconstitution
Prior to administration, dilute in at least 100 mL 0.9% sodium chloride or dextrose 5% water for injection. Although, it is chemically and physically stable when diluted as recommended, sterile precautions should be observed because diluents generally do not contain preservatives.
Administration
IV: All doses should be administered as a slow intravenous infusion (IVPB) over 30 minutes.
Storage
Store at controlled room temperature, 20°C to 25°C (68°F to 77°F); fomepizole solidifies at temperatures <25°C (77°F). If solution becomes solid in the vial, it be should be carefully warmed by running the vial under warm water or by holding in the hand. Solidification does not affect the efficacy, safety, or stability of the drug. Diluted solution should be used within 24 hours and may be stored at room temperature or under refrigeration.
Drug Interactions
There are no known significant interactions.
Adverse Reactions
>10%:
Central nervous system: Headache (14%)
Gastrointestinal: Nausea (11%)
1% to 10% (≤3% unless otherwise noted):
Cardiovascular: Bradycardia, facial flushing, hypotension, phlebitis, shock, tachycardia
Central nervous system: Dizziness (6%), drowsiness (6%), metallic taste (≤6%), agitation, altered sense of smell, anxiety, seizure, speech disturbance, vertigo
Dermatologic: Skin rash
Gastrointestinal: Unpleasant taste (≤6%), abdominal pain, decreased appetite, diarrhea, heartburn, hiccups, vomiting
Genitourinary: Anuria
Hematologic & oncologic: Anemia, disseminated intravascular coagulation (DIC), eosinophilia, lymphangitis
Hepatic: Increased liver enzymes
Local: Application site reaction, inflammation at injection site, pain at injection site
Neuromuscular & skeletal: Back pain
Ophthalmic: Nystagmus, transient blurred vision, visual disturbance
Respiratory: Pharyngitis
Miscellaneous: Fever, multi-organ failure
<1%, postmarketing and/or case reports: Hypersensitivity reaction (mild; mild rash, eosinophilia)
Warnings/Precautions
Disease-related concerns:
- Hepatic impairment: Use with caution in patients with hepatic impairment; metabolized in the liver.
- Renal impairment: Use with caution in patients with renal impairment; fomepizole and its metabolites are excreted in the urine. Hemodialysis should be considered as an adjunct to fomepizole in patients with renal failure, significant acidosis (pH <7.25-7.3), worsening metabolic acidosis, or ethylene glycol or methanol concentrations ≥50 mg/dL.
Special populations:
- Pediatric: Pediatric administration is not FDA approved; however, safe and efficacious use in this patient population for ethylene glycol and methanol intoxication has been reported (Baum, 2000; Benitez, 2000; Boyer, 2001; Brown, 2001; De Brabander, 2005; Detaille, 2004; Fisher, 1998). Consider consultation with a clinical toxicologist or poison control center.
Other warnings/precautions:
- Administration: Should not be given undiluted or by bolus injection.
Monitoring Parameters
Ideally, fomepizole plasma concentrations should be monitored; however, fomepizole concentrations are generally not available.
Use these parameters to monitor the response to fomepizole: Plasma (preferred)/urinary ethylene glycol or methanol concentrations, urinary oxalate (ethylene glycol), plasma (preferred)/urinary osmolality, renal/hepatic function, serum electrolytes, arterial blood gases; anion and osmolar gaps, resolution of clinical signs and symptoms of ethylene glycol or methanol intoxication
Pregnancy
Pregnancy Risk Factor
C
Pregnancy Considerations
Animal reproduction studies have not been conducted. In general, medications used as antidotes should take into consideration the health and prognosis of the mother; antidotes should be administered to pregnant women if there is a clear indication for use and should not be withheld because of fears of teratogenicity (Bailey, 2003).
Patient Education
What is this drug used for?
- It is used to treat methanol or ethylene glycol poisoning.
Frequently reported side effects of this drug
- Headache
- Bad taste
- Dizziness
- Fatigue
- Nausea
Other side effects of this drug: Talk with your doctor right away if you have any of these signs of:
- A significant reaction like wheezing; chest tightness; fever; itching; bad cough; blue skin color; seizures; or swelling of face, lips, tongue, or throat.
Note: This is not a comprehensive list of all side effects. Talk to your doctor if you have questions.
Consumer Information Use and Disclaimer: This information should not be used to decide whether or not to take this medicine or any other medicine. Only the healthcare provider has the knowledge and training to decide which medicines are right for a specific patient. This information does not endorse any medicine as safe, effective, or approved for treating any patient or health condition. This is only a brief summary of general information about this medicine. It does NOT include all information about the possible uses, directions, warnings, precautions, interactions, adverse effects, or risks that may apply to this medicine. This information is not specific medical advice and does not replace information you receive from the healthcare provider. You must talk with the healthcare provider for complete information about the risks and benefits of using this medicine.
