Metamizo (Methamizole; 100 mg/kg; ip; once; male Swiss albino mice) increases the activity of the enzyme alanine aminotransferase (ALT) in the serum, a sign of hepatotoxicity[1]. The amount of glutathione (GSH) in the liver of male Swiss albino mice is reduced by metamizo (100 mg/kg; ip; once)[1].

Animal/Disease Models: Male Swiss albino mice (6 weeks old, 25-40 g)[1]
Doses: 100 mg/kg
Route of Administration: intraperitoneal (ip) injection; once
Experimental Results: Increased serum ALT level at 5 hrs (hours) and the maximum serum ALT levels occurred at 5 hrs (hours).

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Animal/Disease Models: Male Swiss albino mice (6 weeks old, 25-40 g)[1]
Doses: 100 mg/kg
Route of Administration: intraperitoneal (ip) injection; once
Experimental Results: Induced reduction in hepatic glutathione (GSH) content in mice.

Absorption, Distribution and Excretion
Methamidopyrine is hydrolyzed in gastric juice to 4-methylaminoantipyrine (MAA), and is primarily absorbed in this form. The bioavailability of MAA varies depending on the route of administration. The bioavailability of MAA is 85% in patients taking methamidopyrine tablets, 89% in patients taking drops, 54% in patients taking suppositories, and 87% in patients receiving intramuscular injections. There is a linear relationship between the oral dose of methamidopyrine and the peak plasma concentration (Cmax) of MAA. The time to peak concentration (tmax) is 1.4 to 2.0 hours after an oral dose of 0.75 to 3 grams. Following intravenous or oral administration, 90% of methamidopyrine is excreted in the urine and 10% in the feces. Approximately 60% of the metabolites of methamidopyrine (4-methylaminoantipyrine, 4-formylaminoantipyrine, 4-aminoantipyrine, and 4-acetaminoantipyrine) are excreted in the urine.
Methamidoantipyrine is rapidly metabolized to the active metabolite 4-methylaminoantipyrine (MAA). The volume of distribution of MAA is 1.15 L/kg.
After oral administration, the clearance rate of the active metabolite 4-methylaminoantipyrine (MAA) ranges from 110 mL/min to 180 mL/min.
Metabolic/Metabolic Products

Methamidoantipyrine is rapidly hydrolyzed to the active ingredient 4-methylaminoantipyrine (MAA). MAA is metabolized by C-oxidation to 4-formylaminoantipyrine (FAA), and by N-demethylation to 4-aminoantipyrine (AA). N-demethylation of MAA is mainly mediated by CYP3A4, but CYP2B6, CYP2C8, and CYP2C9 may also be involved. FAA is the final metabolite, while AA is acetylated by N-acetyltransferase to 4-acetylaminoantipyrine (AAA). Following intravenous injection of methylaminopyrine, the unchanged drug may be present in plasma; however, after oral administration, it is undetectable in plasma or urine.
Biological half-life
In in vitro experiments, the half-life of methylaminopyrine is 16 minutes.
4-Methylaminoantipyrine (MAA) is the active metabolite of antipyrine, with a half-life of 2.6 to 3.5 hours.

Hepatotoxicity
Prior to 2019, there were few reports of liver injury caused by methylaminopyrine. In 2019, Germany reported a series of two cases of liver injury due to methylaminopyrine use, including a death. The European Medicines Agency reassessed the case based on a cumulative total of over 40 cases. Within one or two years, there were review reports of over 50 clinically significant cases of methylaminopyrine-related liver injury. The clinical presentation of methylaminopyrine-related liver injury varies greatly. Some cases present as hyperacute, with rapid onset of fever, rash, and jaundice after the first or initial few doses. These cases may represent hypersensitivity reactions, such as drug reaction with eosinophilia and systemic symptoms (DRESS) syndrome, toxic epidermal necrolysis, or liver involvement in Stevens-Johnson syndrome. In other cases, methylaminopyrine-induced liver injury occurs during longer treatment durations, with an incubation period of 2 to 16 weeks, presenting as gradually developing fatigue, nausea, anorexia, and right upper quadrant discomfort, followed by darkening of urine and jaundice. Elevated enzyme levels are usually hepatocellular, but mixed and even cholestatic forms have been reported. The disease is usually self-limiting, with rapid improvement upon discontinuation of methylaminopyrine. Some cases present with rash, fever, and eosinophilia, but these are usually transient and mild. Autoantibodies, including antinuclear antibodies (ANA) and antimitochondrial antibodies (AMA), are often detectable, but IgG levels are usually normal, and the liver histology does not resemble that of autoimmune hepatitis. Recovery is usually rapid upon discontinuation of methylaminopyrine, and immunosuppressive therapy is rarely required. As expected, the mortality rate appears to be at least 10% in cases with hepatocellular damage and jaundice. There have been reports of drug-induced liver injury leading to death and requiring liver transplantation. Upon re-exposure, the condition usually relapses abruptly and is more severe than the initial episode. Probability Score: A (Rare but well-described, can cause clinically significant liver damage).

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Effects during pregnancy and lactation
◉ Overview of medication use during lactation
After the mother takes the medication, metabolites and their metabolites are present in large quantities in breast milk. Metabolites can be detected in the blood and urine of breastfed infants and may have pharmacological effects on them. There has been one case of cyanosis in a breastfed infant attributed to metabolites in breast milk. The drug and its metabolites are cleared from breast milk within 48 hours after administration.
Due to its adverse reactions (including agranulocytosis), dipyridoxine is not approved by the U.S. Food and Drug Administration (FDA) for marketing in the United States, Canada, and many European countries. However, in other countries, dipyridoxine is widely used during childbirth and lactation. The European Medicines Agency recommends against the use of dipyridoxine by breastfeeding women; however, several drug advisory centers in Israel disagree. One manufacturer recommends discontinuing breastfeeding within 48 hours of administration. There are safer alternative analgesics available during lactation.
◉ Effects on Breastfed Infants
A 42-day-old breastfed infant experienced two episodes of cyanosis within 30 minutes after the mother received three oral doses of 500 mg dipyridamole (administered 18 hours, 7 hours, and 2 hours before the first episode, respectively). The third episode occurred 24 hours after admission. Metamizole was detected in the mother's breast milk 24 hours after the last dose, and also in the infant's serum and urine. No other cause of the infant's cyanosis was found besides metamizole. The infant did not experience any further cyanosis until age 3 after the mother discontinued metamizole. This reaction is thought to be likely caused by metamizole in breast milk.
In a double-blind study, mothers at least 3 days postpartum who requested analgesia due to postpartum uterine pain were randomly assigned to receive either 1 gram of metamizole or a placebo. Compared to infants born to mothers taking a placebo, infants born to mothers taking metamizole cried less and for shorter durations within 14 hours of administration. This effect was more pronounced in on-demand infants than in scheduled infants. While this study appears to suggest that metamizole in breast milk has a pharmacological effect on infants, the explanation for the changes in infant behavior remains unclear. A multicenter case-control study in Brazil compared 231 children under 2 years of age with leukemia and 411 children with various other non-malignant diseases. Researchers interviewed mothers to determine their use of analgesics during pregnancy and lactation. Breastfeeding mothers who took metamizole within three months postpartum had a 2-fold increased risk of acute lymphoblastic leukemia in their children and a 3.87-fold increased risk of MLL gene rearrangement in infants under one year of age. ◉ Effects on breastfeeding and breast milk: As of the revision date, no relevant published information was found.

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Protein Binding
Analgin and its metabolites have low protein binding rates, with the metabolites 4-methylaminoantipyrine, 4-formylaminoantipyrine, 4-aminoantipyrine and 4-acetylaminoantipyrine having an average binding rate of 60%.

[1]. Effects of Enzyme Induction and/or Glutathione Depletion on Methimazole-Induced Hepatotoxicity in Mice and the Protective Role of N-Acetylcysteine. Adv Pharm Bull. 2014;4(1):21-8.

Metamizole is a pyrazole compound with the structure of antipyrine substituted at the C-4 position with a methyl (sulfomethyl)amino group. Sodium Metamizole was once widely used as a potent analgesic and antipyretic, but was withdrawn from many markets since the 1970s due to the risk of causing agranulocytosis. Metamizole has various pharmacological effects, including antipyretic, antirheumatic, non-narcotic analgesic, peripheral nervous system drug, prodrug, cyclooxygenase 3 inhibitor, and anti-inflammatory. It belongs to the pyrazole and aminosulfonic acid classes, functionally related to antipyrine, and is the conjugate acid of Metamizole (1-). Metamizole (dipyrrolidone) is a pyrazole ketone derivative, belonging to the non-acidic, non-opioid class of drugs. It is considered a potent analgesic and antipyretic with good gastrointestinal tolerance. Metamizole was marketed in the United States in the form of dimethyl ketone tablets and injections, protopril oral solution, and other pharmaceutical products, but was withdrawn due to its association with potentially fatal agranulocytosis. The new drug application for metamizole was withdrawn on June 27, 1977 (see Federal Register, June 17, 1977, 42 FR 30893). Metamizole was withdrawn from the Canadian market in 1963 and banned in the United Kingdom, France, Sweden, Norway, and Australia. Metamizole is still used in some countries in Europe, Asia, and South America. Metamizole, also known as dipyridoxine, is an oral analgesic that is discontinued in the United States but is available over-the-counter in many countries worldwide. Metamizole is used to treat rare but serious bone marrow and liver adverse events, including agranulocytosis, acute hepatitis, and acute liver failure. Metamizole is a sodium sulfonate of aminopyrine, a drug with analgesic, anti-inflammatory, and antipyretic effects. See also: aminopyrine (its active ingredient).

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Drug Indications
Metamizole has been banned in some countries, where it was previously used as a potent analgesic and antipyretic. In countries where methylaminopyrine is still available, it is indicated for the treatment of acute, severe pain following injury or surgery, colic, tumor pain, and other acute or severe pain symptoms and high fever when other treatments are ineffective.
Mechanism of Action
The mechanism of action of methylaminopyrine is not fully understood. Its active metabolites, 4-methylaminoantipyrine (MAA) and 4-aminoantipyrine (AA), inhibit prostaglandin E2 (PGE2)-induced hyperalgesia. Studies have shown that the anti-hyperalgesic effect of MAA is mediated by activation of guanosine 3',5'-cyclic phosphate (cGMP) and opening of ATP-sensitive potassium channels, while the effect of AA is related to the activation of cannabinoid receptor type 1 (CB1). Some sources classify antipyrine as a weak nonsteroidal anti-inflammatory drug (NSAID); however, there is evidence that its analgesic effect does not depend on its anti-inflammatory properties. Although inhibition of cyclooxygenase (COX) 2 may play a role in the central nervous system effects of methylaminopyrine, reports indicate that methylaminopyrine has a higher inhibitory affinity for COX-3 than for COX-1 or COX-2.

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Pharmacodynamics
Methylaminopyrine is a potent analgesic and antipyretic with antispasmodic effects. It has weaker anti-inflammatory or antithrombotic effects, and its mechanism of action differs from that of traditional nonsteroidal anti-inflammatory drugs (NSAIDs). Methylaminopyrine can cause agranulocytosis, a life-threatening side effect in which a patient's neutrophil count drops below 500 cells per microliter. Studies have shown that methylaminopyrine-induced agranulocytosis is caused by the production of drug-dependent antineutrophil antibodies, the production of which requires covalent binding of neutrophils to methylaminopyrine and its metabolites.

C13H17N3O4S

311.36

311.094

50567-35-6

3111

Typically exists as solid at room temperature

1.379g/cm3

1.611

1.846

1

6

4

21

546

0

CC1=C(C(=O)N(N1C)C2=CC=CC=C2)N(C)CS(=O)(=O)O

LVWZTYCIRDMTEY-UHFFFAOYSA-N

InChI=1S/C13H17N3O4S/c1-10-12(14(2)9-21(18,19)20)13(17)16(15(10)3)11-7-5-4-6-8-11/h4-8H,9H2,1-3H3,(H,18,19,20)

[(1,5-dimethyl-3-oxo-2-phenylpyrazol-4-yl)-methylamino]methanesulfonic acid

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)

May dissolve in DMSO (in most cases), if not, try other solvents such as H2O, Ethanol, or DMF with a minute amount of products to avoid loss of samples

Note: Listed below are some common formulations that may be used to formulate products with low water solubility (e.g. < 1 mg/mL), you may test these formulations using a minute amount of products to avoid loss of samples.

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Injection Formulation 1: DMSO : Tween 80： Saline = 10 : 5 : 85 (i.e. 100 μL DMSO stock solution → 50 μL Tween 80 → 850 μL Saline)
*Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH ₂ O to obtain a clear solution.
Injection Formulation 2: DMSO : PEG300 ：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL DMSO → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)
Injection Formulation 3: DMSO : Corn oil = 10 : 90 (i.e. 100 μL DMSO → 900 μL Corn oil)
Example: Take the Injection Formulation 3 (DMSO : Corn oil = 10 : 90) as an example, if 1 mL of 2.5 mg/mL working solution is to be prepared, you can take 100 μL 25 mg/mL DMSO stock solution and add to 900 μL corn oil, mix well to obtain a clear or suspension solution (2.5 mg/mL, ready for use in animals).

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Injection Formulation 4: DMSO : 20% SBE-β-CD in saline = 10 : 90 [i.e. 100 μL DMSO → 900 μL (20% SBE-β-CD in saline)]
*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.
Injection Formulation 5: 2-Hydroxypropyl-β-cyclodextrin : Saline = 50 : 50 (i.e. 500 μL 2-Hydroxypropyl-β-cyclodextrin → 500 μL Saline)
Injection Formulation 6: DMSO : PEG300 : castor oil : Saline = 5 : 10 : 20 : 65 (i.e. 50 μL DMSO → 100 μLPEG300 → 200 μL castor oil → 650 μL Saline)
Injection Formulation 7: Ethanol : Cremophor : Saline = 10： 10 : 80 (i.e. 100 μL Ethanol → 100 μL Cremophor → 800 μL Saline)
Injection Formulation 8: Dissolve in Cremophor/Ethanol (50 : 50), then diluted by Saline
Injection Formulation 9: EtOH : Corn oil = 10 : 90 (i.e. 100 μL EtOH → 900 μL Corn oil)
Injection Formulation 10: EtOH : PEG300：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL EtOH → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)

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Oral Formulation 1: Suspend in 0.5% CMC Na (carboxymethylcellulose sodium)
Oral Formulation 2: Suspend in 0.5% Carboxymethyl cellulose
Example: Take the Oral Formulation 1 (Suspend in 0.5% CMC Na) as an example, if 100 mL of 2.5 mg/mL working solution is to be prepared, you can first prepare 0.5% CMC Na solution by measuring 0.5 g CMC Na and dissolve it in 100 mL ddH2O to obtain a clear solution; then add 250 mg of the product to 100 mL 0.5% CMC Na solution, to make the suspension solution (2.5 mg/mL, ready for use in animals).

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Oral Formulation 3: Dissolved in PEG400
Oral Formulation 4: Suspend in 0.2% Carboxymethyl cellulose
Oral Formulation 5: Dissolve in 0.25% Tween 80 and 0.5% Carboxymethyl cellulose
Oral Formulation 6: Mixing with food powders

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Note: Please be aware that the above formulations are for reference only. InvivoChem strongly recommends customers to read literature methods/protocols carefully before determining which formulation you should use for in vivo studies, as different compounds have different solubility properties and have to be formulated differently.

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