Non-selective cyclooxygenase (COX) inhibitor (inhibits both COX-1 and COX-2). The ratio of log IC50 values for COX-1/COX-2 binding affinity derived from a human whole blood assay is provided in Figure 1, but specific IC50 values for diflunisal are not given in the text. [3]

Rats given increasing dosages of diflunisal showed that the pharmacokinetics of the drug are complexly influenced by dose. Diflunisal exhibits an exponential drop in plasma concentration over time, whereas its half-life increases when the dosage is increased. When the dose was increased from 3 to 10 mg/kg, CLP dramatically dropped and subsequently stayed mostly stable throughout the 10 mg/kg to 60 mg/kg treatment range. It has been demonstrated that diflunisal binds strongly and concentration-dependently to the plasma proteins of rats. In the range of 5 to 300 μg/mL, there was an approximate 10-fold increase in the proportion of unbound diflunisal [1]. Following oral administration, diflunisal has an activity that is roughly 25 times more than aspirin, 3 times greater than glafenine, and 2 times greater than zomelar [2].

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Administration of diflunisal to pregnant rats at 250 mg/kg/day on gestational days (GD) 9 and 10 resulted in an increased incidence of ventricular septal defects (VSD) in fetuses (8 fetuses from 7 litters). [3]
Administration of diflunisal to pregnant rabbits at 250 mg/kg/day on GDs 9, 10, and 11 induced diaphragmatic hernia (DH), VSD, and midline defects (MD; omphalocele), as well as microphthalmia and accessory blood vessels in fetuses. [3]

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Administration of diflunisal to pregnant rats at 250 mg/kg/day on gestational days (GD) 9 and 10 resulted in an increased incidence of ventricular septal defects (VSD) in fetuses (8 fetuses from 7 litters). [3]
Administration of diflunisal to pregnant rabbits at 250 mg/kg/day on GDs 9, 10, and 11 induced diaphragmatic hernia (DH), VSD, and midline defects (MD; omphalocele), as well as microphthalmia and accessory blood vessels in fetuses. [3]

Diflunisal was suspended daily in a 0.5% aqueous methylcellulose solution. [3]
Pregnant rats were administered diflunisal orally by gavage at 250 mg/kg/day (10 ml/kg body weight) on GDs 9 and 10. [3]
Pregnant rabbits were administered diflunisal orally by gavage at 250 mg/kg/day (2 ml/kg body weight) on GDs 9, 10, and 11. [3]
Fetuses were collected by cesarean section on GD 21 (rats) and GD 29 (rabbits) and examined for external and visceral developmental anomalies. [3]

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Diflunisal was suspended daily in a 0.5% aqueous methylcellulose solution. [3]
Pregnant rats were administered diflunisal orally by gavage at 250 mg/kg/day (10 ml/kg body weight) on GDs 9 and 10. [3]
Pregnant rabbits were administered diflunisal orally by gavage at 250 mg/kg/day (2 ml/kg body weight) on GDs 9, 10, and 11. [3]
Fetuses were collected by cesarean section on GD 21 (rats) and GD 29 (rabbits) and examined for external and visceral developmental anomalies. [3]

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 can 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 can also be mixed. 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 case series of drug-induced liver injury or acute liver failure. Probability Score: C (may lead to clinically significant liver injury). Pregnancy and Lactation Effects ◉ 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 newborns or premature infants, especially nursing women, a shorter duration of action and more published information may be preferred. ◉ Effects on Breastfed Infants No published information found as of the revision date. ◉ Effects on Lactation and Breast Milk No published information found as of the revision date.

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Protein binding
At least 98% to 99% of diflunisal in plasma is bound to proteins.

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Toxicity data
LD50: 392 mg/kg (oral, rat) (A308)
LD50: 439 mg/kg (oral, mouse) (A308)
LD50: 603 mg/kg (oral, rabbit) (A308)

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Diflunisal Causes maternal toxicity In rats, diflunisal caused gastrointestinal toxicity (gastrointestinal adhesions, gastrointestinal dilatation, mesenteric lymphadenopathy), weight loss, and reduced food intake. Three rats experienced maternal death. [3]
In rabbits, diflunisal caused maternal death (4 female rabbits died or were euthanized), loose/watery stools, decreased activity, increased respiration, weight loss, and reduced food intake. [3]

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Diflunisal caused maternal toxicity in rats, including gastrointestinal toxicity (gastrointestinal adhesions, gastrointestinal dilatation, mesenteric lymphadenopathy), weight loss, and decreased food intake. Three rats died as a result. [3] In rabbits, diflunisal caused maternal death (four maternal rabbits died or were euthanized), loose/watery stools, decreased activity, rapid breathing, weight loss, and decreased food intake. [3]

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

[2]. 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.

[3]. 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.

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

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Diflunisal is a nonsteroidal anti-inflammatory drug (NSAID) with nonselective cyclooxygenase (COX) inhibitory activity. [3]
During sensitive periods of heart development and midline closure, administration of diflunisal to rats and rabbits can lead to fetal developmental defects (ventricular septal defect, diaphragmatic hernia, cardiomyopathy). [3]
Studies have shown that COX-1 inhibition may be involved in the development of ventricular septal defects, while selective COX-2 inhibition appears to have no effect on cardiac development or midline closure. [3]

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Diflunisal is a nonsteroidal anti-inflammatory drug (NSAID) with nonselective cyclooxygenase (COX) inhibitory activity. [3]
Administration of this drug to rats and rabbits during sensitive periods of cardiac development and midline closure is associated with fetal developmental defects (ventricular septal defects, diaphragmatic hernia, cardiomyopathy). [3]
This study suggests that COX-1 inhibitors may be involved in the induction of ventricular septal defects, while selective COX-2 inhibitors appear to have no effect on cardiac development or midline closure. [3]

C13H8F2O3

250.1976

250.044

22494-42-4

Diflunisal-d3;1286107-99-0

3059

White to off-white solid powder

1.4±0.1 g/cm3

386.9±42.0 °C at 760 mmHg

32-36 °C

187.8±27.9 °C

0.0±0.9 mmHg at 25°C

1.601

4.44

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)

2',4'-difluoro-4-hydroxy-[1,1'-biphenyl]-3-carboxylic acid

MK-647; MK647; MK 647; trade names: Dolobid; Dolobis; Flovacil; Fluniget; Fluodonil; Dflunisal

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)

DMSO : ~50 mg/mL (~199.84 mM)

Solubility in Formulation 1: ≥ 2.5 mg/mL (9.99 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 (9.99 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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 (Please use freshly prepared in vivo formulations for optimal results.)