Drug compounds have included stable heavy isotopes of carbon, hydrogen, and other elements, mostly as quantitative tracers while the drugs were being developed. Because deuteration may have an effect on a drug's pharmacokinetics and metabolic properties, it is a cause for concern [1].

Absorption, Distribution and Excretion
The drug is rapidly and completely absorbed after oral administration, with a bioavailability of 80-90%. Peak plasma concentrations are reached 2-3 hours after oral administration. Approximately 90% of the administered dose is excreted in the urine as two soluble glucuronide conjugates. Diflunisal is almost entirely eliminated in feces. Metabolism/Metabolites The drug is primarily metabolized in the liver, specifically as glucuronide conjugates (90% of the administered dose). Elimination pathway: The drug is excreted in the urine as two soluble glucuronide conjugates, approximately 90% of the administered dose. Diflunisal is almost entirely eliminated in feces. Half-life: 8 to 12 hours. Biological half-life 8 to 12 hours

Toxicity Summary
The exact mechanism of diflunisal's analgesic and anti-inflammatory effects is unclear. Diflunisal is a prostaglandin synthase inhibitor. In animal studies, prostaglandins sensitize afferent nerves and enhance bradykinin-induced pain. Since prostaglandins are known mediators of pain and inflammation, diflunisal's mechanism of action may be related to a reduction in prostaglandins in peripheral tissues. Hepatotoxicity
Diflunisal treatment has been reported to be associated with a low incidence of asymptomatic and transient elevations in serum transaminases, which may subside even with continued use. Significant transaminase elevations (more than 3-fold) are rare. Clinically significant liver injury with jaundice caused by diflunisal is uncommon; only case reports exist. However, the clinical and histological features of diflunisal hepatotoxicity are unique, resembling immune-mediated allergic hepatitis, which is distinctly different from liver injury caused by aspirin or other salicylates (Case 1). The latency period is 1 to 4 weeks, and the pattern of enzyme elevation is usually cholestatic, but mixed patterns are also possible. Most patients experience immune hypersensitivity symptoms such as rash, fever, and joint pain; eosinophilia or atypical lymphocytosis are also common. No aspirin allergy history has been reported in cases of diflunisal hypersensitivity. Diflunisal is not a commonly used drug and has not been mentioned in large series of cases of drug-induced liver injury or acute liver failure.
Probability Score: C (May cause clinically significant liver injury).

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Effects during pregnancy and lactation
◉ Overview of use during lactation
Small amounts of diflunisal in breast milk do not appear to pose a serious risk to nursing infants. However, for nursing newborns or premature infants, a drug with a shorter duration of action and more published information may be preferred.
◉ Effects on breastfed infants
No relevant published information found as of the revision date.
◉ Effects on lactation and breast milk
No relevant published information found as of the revision date. Protein Binding: At least 98% to 99% of diflunisal in plasma is bound to proteins. Toxicity Data: LD50: 392 mg/kg (oral, rat) (A308) LD50: 439 mg/kg (oral, mouse) (A308) LD50: 603 mg/kg (oral, rabbit) (A308)

[1]. Impact of Deuterium Substitution on the Pharmacokinetics of Pharmaceuticals. Ann Pharmacother. 2019;53(2):211-216.

[2]. Dose-dependent pharmacokinetics of diflunisal in rats: dual effects of protein binding and metabolism. J Pharmacol Exp Ther. 1985 Nov;235(2):402-6.

[3]. Analgesic activity of diflunisal [MK-647; 5-(2,4-difluorophenyl)salicylic acid] in rats with hyperalgesia induced by Freund's adjuvant. J Pharmacol Exp Ther. 1979 Dec;211(3):678-85.

[4]. Relationship between cyclooxygenase 1 and 2 selective inhibitors and fetal development when administered to rats and rabbits during the sensitive periods for heart development and midline closure. Birth Defects Res B Dev Reprod Toxicol. 2003 Feb;68(1):47-56.

According to state or federal labeling requirements, diflunisal can cause developmental toxicity and female reproductive toxicity. Diflunisal is an organofluorine compound composed of salicylic acid with a 2,4-difluorophenyl group linked at the 5-position. It is a nonsteroidal anti-inflammatory drug (NSAID) and a non-narcotic analgesic. It is an organofluorine compound and a monohydroxybenzoic acid. Its function is related to salicylic acid and 1,3-difluorobenzene. Diflunisal is a salicylate derivative and a NSAID with pharmacological effects similar to other typical NSAIDs. Diflunisal has anti-inflammatory, analgesic, and antipyretic effects. Although its mechanism of action is not fully elucidated, much of its action appears to be related to the inhibition of prostaglandin synthesis via the arachidonic acid pathway. Diflunisal is used to relieve pain caused by inflammation and to treat symptoms of rheumatoid arthritis and osteoarthritis. Diflunisal is a nonsteroidal anti-inflammatory drug. Its mechanism of action is as a cyclooxygenase inhibitor. Diflunisal is a salicylic acid derivative used to treat chronic arthritis and mild to moderate acute pain. Diflunisal is associated with mild, transient increases in serum transaminase levels during treatment and rare drug-induced liver disease. Diflunisal is a difluorophenyl derivative of salicylic acid and is a nonsteroidal anti-inflammatory drug (NSAID) with antipyretic, analgesic, and anti-inflammatory effects. Diflunisal competitively inhibits cyclooxygenases (COX)-1 and -2, with a higher affinity for COX-1, thereby blocking the conversion of arachidonic acid to prostaglandin precursors. This leads to inhibition of prostaglandin production involved in pain, inflammation, and fever. Unlike other salicylates, diflunisal is not metabolized to salicylic acid, thus having a longer half-life. Diflunisal is a salicylate derivative belonging to the NSAID class, and its pharmacological effects are similar to other typical NSAIDs. Diflunisal has anti-inflammatory, analgesic, and antipyretic effects. Although its mechanism of action is not fully elucidated, much of its effect appears to be related to the inhibition of prostaglandin synthesis via the arachidonic acid pathway. Diflunisal is used to relieve pain caused by inflammation, and to treat symptoms of rheumatoid arthritis and osteoarthritis. It is a salicylate derivative with anti-inflammatory and analgesic effects, similar to aspirin in its effects and side effects. See also: Diflunisal sodium (its active ingredient). Indications: For the treatment of mild to moderate pain associated with inflammation (e.g., musculoskeletal trauma, post-tooth extraction, post-episiotomy), symptoms of osteoarthritis, and rheumatoid arthritis. FDA label. Mechanism of Action: The exact mechanism of action of diflunisal's analgesic and anti-inflammatory effects is unclear. Diflunisal is a prostaglandin synthase inhibitor. In animals, prostaglandins sensitize afferent nerves and enhance the pain-inducing effects of bradykinin. Since prostaglandins are known mediators of pain and inflammation, diflunisal's mechanism of action may be related to its reduction of prostaglandin levels in peripheral tissues.

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Pharmacodynamics
Diflunisal is a nonsteroidal anti-inflammatory drug (NSAID) with analgesic, anti-inflammatory, and antipyretic effects. It is a peripherally acting, non-narcotic analgesic. There are no reports of habituation, tolerance, or addiction. Diflunisal is a difluorophenyl derivative of salicylic acid. Chemically, diflunisal differs from aspirin (acetylsalicylic acid) in two ways. First, diflunisal has a difluorophenyl substituent on carbon atom 1. Second, diflunisal has lost the O-acetyl group on carbon atom 4. Diflunisal is not metabolized to salicylic acid, and the fluorine atom does not detach from the difluorophenyl ring structure.

C13H8F2O3

250.197630882263

250.044

1286107-99-0

Diflunisal;22494-42-4

3059

Typically exists as solid at room temperature

210-211
210 - 221 °C

4.4

2

5

2

18

311

0

HUPFGZXOMWLGNK-UHFFFAOYSA-N

InChI=1S/C13H8F2O3/c14-8-2-3-9(11(15)6-8)7-1-4-12(16)10(5-7)13(17)18/h1-6,16H,(H,17,18)

5-(2,4-difluorophenyl)-2-hydroxybenzoic 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.)