The precise mechanism of the analgesic and anti-inflammatory actions of diflunisal is not known. Diflunisal is a prostaglandin synthetase inhibitor. In animals, prostaglandins sensitize afferent nerves and potentiate the action of bradykinin in inducing pain. Since prostaglandins are known to be among the mediators of pain and inflammation, the mode of action of diflunisal may be due to a decrease of prostaglandins in peripheral tissues.
Diflunisal is a nonsteroidal drug with analgesic, anti-inflammatory and antipyretic properties. It is a peripherally-acting non-narcotic analgesic drug. Habituation, tolerance and addiction have not been reported. Diflunisal is a difluorophenyl derivative of salicylic acid. Chemically, diflunisal differs from aspirin (acetylsalicylic acid) in two respects. The first of these two is the presence of a difluorophenyl substituent at carbon 1. The second difference is the removal of the 0-acetyl group from the carbon 4 position. Diflunisal is not metabolized to salicylic acid, and the fluorine atoms are not displaced from the difluorophenyl ring structure.
Hepatic, primarily via glucuronide conjugation (90% of administered dose).
Oral LD50 in rat, mouse, and rabbit is 392 mg/kg, 439 mg/kg, and 603 mg/kg, respectively. Symptoms of overdose include drowsiness, nausea, vomiting, diarrhea, hyperventilation, tachycardia, sweating, tinnitus, disorientation, stupor, and coma. The lowest dose without the presence of other medicines which caused death was 15 grams. Selective COX-2 inhibitors have been associated with increased risk of serious cardiovascular events (e.g. myocardial infarction, stroke) in some patients. Current data is insufficient to assess the cardiovascular risk of diflunisal. Short-term use does not appear to be associated with increased cardiovascular risk (except when used immediately following coronary artery bypass graft (CABG) surgery). Risk of GI toxicity including bleeding, ulceration and perforation. Risk of direct renal injury, including renal papillary necrosis. Severe hepatic reactions, including cholestasis and/or jaundice, have been reported. May cause rash or hypersensitivity syndrome.