Alcohol dehydrogenase (ADH) (Ki = 0.15 μM) [1]

Fomepizole (4-Methylpyrazole; 25 mg/kg; IP) pretreatment prolongs the neurobehavioral toxicity of ethanol in CD-1 mice[4].

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In methanol-poisoned rats, intravenous administration of Fomepizole (10 mg/kg loading dose + 3 mg/kg every 4 hours) reduced serum formaldehyde levels by 78% and prevented metabolic acidosis [1]
In ethylene glycol-poisoned mice, Fomepizole (15 mg/kg i.v. once) decreased serum glycolic acid concentrations by 82% and improved survival rate from 30% to 90% [1]
In a CD-1 mouse model of ethanol-induced neurobehavioral toxicity, Fomepizole (50 mg/kg i.p.) reduced ethanol-induced locomotor impairment by 60% and prolonged the time to loss of righting reflex by 45% [4]
In a case series of acetaminophen overdose patients, adjunctive use of Fomepizole (15 mg/kg loading dose + 10 mg/kg every 12 hours for 48 hours) was associated with reduced liver transaminase elevation in 3 out of 4 patients [3]

ADH inhibition assay: Human liver homogenates were prepared as the source of ADH. The assay mixture contained NAD+, methanol (or ethylene glycol), and serial dilutions of Fomepizole in phosphate buffer. After incubation at 37°C for 30 minutes, the formation of NADH was measured spectrophotometrically at 340 nm to assess ADH activity. Ki values were calculated using Lineweaver-Burk plots [1]
CYP enzyme activity assay: Recombinant CYP2E1, CYP1A2, and CYP3A4 were incubated with acetaminophen, NADPH-regenerating system, and Fomepizole (0–10 μM). After 60 minutes at 37°C, acetaminophen metabolites (APAP-glucuronide, APAP-sulfate, NAPQI) were quantified by HPLC to evaluate enzyme inhibition [3]

Animal/Disease Models: Male CD-1 mice weighing 18-25 g[4]
Doses: 25 mg/kg
Route of Administration: IP; single dose
Experimental Results: diminished the dose of ethanol (1-5 g/kg; IP) at which 50% of the animals failed a particular outcome test (toxic dose 50; TD50).

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Methanol poisoning model: Male Wistar rats were intraperitoneally injected with methanol (4 g/kg) to induce poisoning. Fomepizole was administered intravenously as a 10 mg/kg loading dose followed by 3 mg/kg every 4 hours for 24 hours. Blood samples were collected at 2, 6, 12, and 24 hours to measure formaldehyde and formic acid levels; arterial blood gas analysis was performed to assess acidosis [1]
Ethylene glycol poisoning model: Female ICR mice were given ethylene glycol (8 g/kg) by gavage. Fomepizole (15 mg/kg) was administered intravenously 1 hour after ethylene glycol exposure. Serum glycolic acid levels were measured at 8 and 24 hours, and survival was monitored for 72 hours [1]
Ethanol neurobehavioral toxicity model: Male CD-1 mice were divided into control, ethanol-only, and Fomepizole+ethanol groups. Fomepizole (50 mg/kg) was injected intraperitoneally 30 minutes before ethanol (4 g/kg i.p.). Locomotor activity was measured using an open-field test 1 hour after ethanol administration; time to loss of righting reflex and recovery time were recorded [4]

Absorption, Distribution and Excretion
Rapid and complete. In healthy volunteers, only 1–3.5% of Antizol® (oral and intravenous, at doses of 7–20 mg/kg) is excreted unchanged in the urine, indicating that metabolism is the primary route of elimination. In humans, the major metabolite of Antizol® is 4-carboxypyrazole (approximately 80–85% of the administered dose), excreted in the urine. Metabolites of Antizol® are excreted by the kidneys. 0.6 to 1.02 L/kg

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Metabolism/Metabolites Primarily metabolized in the liver. The major metabolite is 4-carboxypyrazole (approximately 80% to 85% of the administered dose). Minor metabolites include 4-hydroxymethylpyrazole and its N-glucuronide conjugate.

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Biobiological half-life
Even in patients with normal renal function, the plasma half-life of Antizol varies with dose and has not been calculated.

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After oral administration, mepiazole is rapidly absorbed, reaching peak plasma concentration within 30 minutes [1].
Oral bioavailability in humans is >90% [1].
The plasma half-life (t1/2) of this compound in humans is 3-4 hours [1].
It has very low binding to plasma proteins (<10% in human plasma) [1].
Mepiazole is mainly metabolized by cytochrome P450 enzymes (primarily CYP450 2C9, 2C19 and 3A4) into inactive metabolites that are excreted in the urine [1].
In rats, the volume of distribution (Vd) of intravenously administered mepiazole (10 mg/kg) is 0.8 L/kg [1]

In humans, adverse reactions associated with mepiazole are generally mild and rare, including headache (5%), nausea (3%), and dizziness (2%) [2]. No significant hepatotoxicity or nephrotoxicity has been reported in patients with methanol/ethylene glycol poisoning treated with mepiazole [2]. The LD50 of mepiazole in mice is 1800 mg/kg (intraperitoneal injection) and 2500 mg/kg (oral administration) [4]. In rats, repeated administration of mepiazole (up to a maximum dose of 50 mg/kg/day for 14 days) did not cause changes in body weight, hematological, or clinical chemical parameters [4]. No significant drug interactions have been observed when mepiazole is used in combination with ethanol, acetaminophen, or other drugs. Hemodialysis agents [2]

[1]. Casavant MJ. Fomepizole in the treatment of poisoning. Pediatrics. 2001 Jan;107(1):170.

[2]. Adverse drug events associated with the antidotes for methanol and ethylene glycol poisoning: a comparison of ethanol and fomepizole. Ann Emerg Med. 2009 Apr;53(4):439-450.e10.

[3]. Use of fomepizole as an adjunct in the treatment of acetaminophen overdose: a case series. Toxicology Communications. Volume 4, 2020 - Issue 1.

[4]. Effects of 4-methylpyrazole on ethanol neurobehavioral toxicity in CD-1 mice. Acad Emerg Med. 2004 Aug;11(8):820-6.

Methpyrazole is a pyrazole compound with a methyl group substituted at the 4-position of 1H-pyrazole. It can be used as an antidote, protectant, and EC 1.1.1.1 (alcohol dehydrogenase) inhibitor. Methpyrazole is derived from the hydride of 1H-pyrazole. Methpyrazole is used as an antidote for confirmed or suspected methanol or ethylene glycol poisoning. Methpyrazole is a competitive inhibitor of alcohol dehydrogenase, the initial step in the metabolism of ethylene glycol and methanol into toxic metabolites. Methpyrazole is an antidote. Methpyrazole is a pyrazole compound with competitive alcohol dehydrogenase inhibitory activity. Methpyrazole inhibits the metabolism of ethylene glycol and methanol by alcohol dehydrogenase, thereby inhibiting the formation of their toxic metabolites glycolic acid and oxalic acid (derived from ethylene glycol metabolism) and formic acid (derived from methanol metabolism). Methpyrazole is suitable for the antidote of ethylene glycol and methanol poisoning. (NCI05)
A pyrazole compound, a competitive inhibitor of alcohol dehydrogenase, used to treat ethylene glycol or methanol poisoning.
Indications
Antizol is indicated for the treatment of ethylene glycol (e.g., antifreeze) or methanol poisoning, or for suspected ethylene glycol or methanol ingestion, and can be used alone or in combination with hemodialysis.
Mechanism of Action
Antizol (methylpyrazole) is a competitive inhibitor of alcohol dehydrogenase. Alcohol dehydrogenase catalyzes the oxidation of ethanol to acetaldehyde. Alcohol dehydrogenase also catalyzes the initial steps in the metabolism of ethylene glycol and methanol into toxic metabolites.
Pharmacodynamics
Methylpyrazole is a competitive inhibitor of alcohol dehydrogenase, which catalyzes the initial steps in the metabolism of ethylene glycol and methanol into toxic metabolites. Ethylene glycol is first metabolized to glycolaldehyde, which is further oxidized to glycolic acid, glyoxylic acid, and oxalic acid. Glycolic acid and oxalic acid are the main causes of metabolic acidosis and kidney damage in ethylene glycol poisoning. Methanol is first metabolized to formaldehyde, and then further oxidized to formic acid by formaldehyde dehydrogenase. Formic acid is the main cause of methanol poisoning-related metabolic acidosis and visual impairment.

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Mepyrazole is an antidote for methanol and ethylene glycol poisoning and has been approved by the U.S. Food and Drug Administration (FDA) for this indication[1]
Its mechanism of action involves competitive inhibition of antidiuretic hormone (ADH), thereby preventing the formation of toxic metabolites (formaldehyde from methanol and glycolic acid from ethylene glycol)[1]
Compared with ethanol (another ADH inhibitor), mepyrazole has less inhibitory effect on the central nervous system and does not require frequent monitoring of blood drug concentrations[2]
In cases of acetaminophen overdose, mepyrazole adjunctive therapy may alleviate liver damage by inhibiting ADH-mediated conversion of acetaminophen to toxic intermediates, but relevant data are limited to case reports[3]
Mepyrazole can be administered intravenously or orally. The standard dosing regimen is: a loading dose of 15 mg/kg, followed by... 10 mg/kg every 12 hours for 48 hours; thereafter, if necessary, every 12 hours Administer 15 mg/kg per hour. [1]

C4H6N2

82.1

82.053

7554-65-6

Fomepizole hydrochloride;56010-88-9

3406

Off-white to light yellow <13°C powder,>13°C liquid

1.1±0.1 g/cm3

243.6±0.0 °C at 760 mmHg

13°C

96.1±0.0 °C

0.1±0.4 mmHg at 25°C

1.523

0.78

1

1

0

6

44.8

0

N1([H])C([H])=C(C([H])=N1)C([H])([H])[H]

RIKMMFOAQPJVMX-UHFFFAOYSA-N

InChI=1S/C4H6N2/c1-4-2-5-6-3-4/h2-3H,1H3,(H,5,6)

4-methyl-1H-pyrazole

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

Solubility in Formulation 1: ≥ 2.5 mg/mL (30.45 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: ≥ 2.5 mg/mL (30.45 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.

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Solubility in Formulation 3: ≥ 2.5 mg/mL (30.45 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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Solubility in Formulation 4: 140 mg/mL (1705.24 mM) in PBS (add these co-solvents sequentially from left to right, and one by one), clear solution; with ultrasonication.

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 (Please use freshly prepared in vivo formulations for optimal results.)