ANTIZOL
Clinical safety rating: caution
Comprehensive clinical and safety monograph for ANTIZOL (ANTIZOL).
Antizol (fomepizole) is a competitive inhibitor of alcohol dehydrogenase, the enzyme that catalyzes the oxidation of ethanol to acetaldehyde. It also inhibits the metabolism of ethylene glycol and methanol to their toxic metabolites.
| Metabolism | Fomepizole is metabolized primarily in the liver by oxidation via cytochrome P450 enzymes (CYP2E1, CYP1A2, CYP3A4) to 4-carboxypyrazole and other metabolites. It also induces its own metabolism with repeated dosing. |
| Excretion | Renal: 80-95% as parent drug and metabolites. Fecal: <5%. Biliary excretion is negligible. |
| Half-life | Terminal elimination half-life: 2.5-3.5 hours in adults. Clinical context: Dose adjustment recommended in severe renal impairment (CrCl <30 mL/min) due to prolonged half-life. |
| Protein binding | 95% bound primarily to albumin. |
| Volume of Distribution | 0.8-1.0 L/kg. Clinically indicates extensive distribution into total body water and tissues. |
| Bioavailability | Oral: 60-70% (due to first-pass metabolism). |
| Onset of Action | IV: 30 minutes. Oral: 1-2 hours. |
| Duration of Action | IV: 6-8 hours. Oral: 8-12 hours. Duration may be prolonged in hepatic impairment due to reduced metabolism. |
| Molecular Weight | 82.1 |
Initial: 15 mg/kg IV over 10 minutes, then 3 mg/kg IV every 4 hours for 2 doses, then 3 mg/kg IV every 6 hours for 4 doses.
| Dosage form | INJECTABLE |
| Renal impairment | No adjustment required for renal impairment; hemodialysis: 3 mg/kg IV after each dialysis session. |
| Liver impairment | No official guidelines; use with caution in severe hepatic impairment due to limited data. |
| Pediatric use | Initial: 15 mg/kg IV over 10 minutes, then 3 mg/kg IV every 4 hours for 2 doses, then 3 mg/kg IV every 6 hours for 4 doses; maximum single dose 1500 mg. |
| Geriatric use | No specific adjustment; monitor renal function and consider reduced initial dose (e.g., 7.5 mg/kg) due to age-related decreased clearance. |
| 1st trimester | Fomepizole (ANTIZOL) is not recommended during first trimester unless benefit outweighs risk; animal studies show fetal harm at high doses. |
| 2nd trimester | Limited human data; use only if clearly needed due to potential fetal toxicity from ethylene glycol/methanol poisoning itself. |
| 3rd trimester | Similar to t2; avoid unless maternal benefit justifies potential fetal risk. |
Clinical note
Comprehensive clinical and safety monograph for ANTIZOL (ANTIZOL).
| Placental transfer | Fomepizole crosses the placenta in animal studies; human data are limited, but transfer is expected given its molecular size. |
| Breastfeeding | Fomepizole is excreted into breast milk in low amounts; however, due to theoretical risk of infant toxicity, caution is advised. Use only if essential, and monitor infant for adverse effects. |
■ FDA Black Box Warning
No FDA black box warnings.
| Serious Effects |
Known hypersensitivity to fomepizole or any component of the formulation
| Precautions | Monitor for hypersensitivity reactions, including rash and eosinophilia., Use with caution in patients with known hypersensitivity to pyrazole compounds., Monitor liver function tests as fomepizole may cause elevations in transaminases., Fomepizole is dialyzable; dose adjustment may be needed during hemodialysis., Should not be used as a substitute for hemodialysis in severe poisoning. |
| Food/Dietary | No specific food interactions are known. However, alcohol consumption must be strictly avoided during therapy due to the risk of disulfiram-like reactions and competition for alcohol dehydrogenase. |
Loading safety data…
| Lactation Rating | L3 (Moderately Safe) |
| Teratogenic Risk | ANTIZOL (fomepizole) is FDA Pregnancy Category C. First trimester: Data limited; animal studies show fetal toxicity at high doses. Second/third trimesters: Avoid unless benefit outweighs risk; no known teratogenicity in humans. |
| Fetal Monitoring | Monitor maternal liver and renal function, electrolytes, coagulation parameters. Fetal monitoring: ultrasonography for growth and anatomy if exposure during pregnancy. |
| Fertility Effects | No human data on fertility impairment. Animal studies show no significant reproductive effects at clinically relevant doses. |
| Clinical Pearls | ANTIZOL (fomepizole) is a potent alcohol dehydrogenase inhibitor used for methanol or ethylene glycol poisoning. Administer intravenously; loading dose 15 mg/kg, then 10 mg/kg every 12 hours for 4 doses, then 15 mg/kg every 12 hours thereafter. Monitor serum osmolal gap and metabolic acidosis to guide therapy. In patients with suspected toxic alcohol ingestion, empiric therapy prior to confirmatory labs is warranted if clinical suspicion is high. Hemodialysis may be needed for severe poisoning (e.g., high levels, renal failure, severe acidosis). Fomepizole is preferred over ethanol due to fewer adverse effects and easier dosing. |
| Patient Advice | This medication is only used in a hospital setting for certain types of poisoning. · You will receive this drug through a vein (IV) and your vital signs and blood levels will be closely monitored. · Common side effects include headache, nausea, dizziness, and injection site reactions; report any unusual symptoms to your healthcare team immediately. · Do not consume any alcohol during treatment, as it can interfere with the medication's effect and worsen side effects. · Inform your doctor if you have a history of allergy to fomepizole or any other medications. |