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Systematic (IUPAC) name
5-(2,4-difluorophenyl)-2-hydroxy-benzoic acid
CAS number 22494-42-4
ATC code N02BA11
PubChem 3059
DrugBank APRD00922
Chemical data
Formula C13H8F2O3 
Mol. mass 250.198 g/mol
Pharmacokinetic data
Bioavailability 80-90%
Protein binding >99%
Metabolism Hepatic
Half life 8 to 12 hours
Excretion Renal
Therapeutic considerations
Pregnancy cat.


Legal status

POM(UK) -only(US)

Routes Oral

Diflunisal is a generic NSAID (non-steroidal anti-inflammatory drug). It is often used under the brand name Dolobid marketed by Merck & Co. Diflunisal acts by inhibiting the production of prostaglandin, a hormone that creates inflammation and stimulates the neuro receptors for pain. Though diflunisal has an onset of 1 hour, and maximum analgesia at 2 to 3 hours, the diflunisal plasma levels will not be steady until repeated doesages are achieved. To increase the rate at which the diflunisal plasma levels become steady, a loading dose is usually used. It is primarily used to treat symptoms of arthritis.


Deaths that have occurred from diflunisal usually involved mixed drugs and or extremely high dosages. The oral LD50 is 500 mg/kg. Symptoms of overdose include, coma, tachycardia, stupor, and vomiting. The lowest dose without the presence of other medicines which caused death was 15 grams. Mixed with other medicines, a death at 7.5 grams has also occurred. Diflunisal usually comes in 250 or 500 mg, thus it is relatively hard to overdose by accident.


This medication has no side effects like those of recreational drugs.

Indicated for:
  • Pain, mild-moderate
  • Osteoarthritis
  • Rheumatoid arthritis
  • Injury to tendons
  • Inflammation

Do not cut/crush/chew. Monitor blood pressure. Use lowest effective dose for shortest duration.

Side effects:


  • Irregular heart beat (!)
  • This medication may increase risk of serious and potentially fatal cardiovascular thrombotic events, MI, and stroke (!)
  • Risk may increase with duration of use (!)
  • Increased risk for Cardiovascular disease history (!)
  • Contraindicated for Heart Bypass peri-op pain (!)

Ear, nose, and throat:

  • Ringing in the ears (!)


  • Yellowing of eyes (!)


  • Increased risk of serious GI adverse events including bleeding, ulceration, and stomach or intestine perforation which can be fatal: may occur at any time during use and without warning. Elderly at greater risk for serious GI events (!)
  • Abdominal pain and cramps
  • Constipation
  • Gas & Flatulence
  • Diarrhea
  • Nausea & Vomiting
  • Dyspepsia

Central Nervous System:

  • Drowsiness
  • Dizziness
  • Headache
  • Insomnia
  • Fatigue
  • Somnolence


  • Nervousness


  • Swelling of the feet, ankles, lower legs, and hands (!)
  • Yellowing of skin (!)
  • Rash
  • Ecchymosis


  • Hypersensitivity to aspirin/NSAID-induced asthma or urticaria
  • Aspirin triad
  • Pregnancy 3rd trimester
  • CABG surgery (peri-op pain)


  • Cardiovascular disease
  • Cardiac risk factors
  • Hypertension
  • Congestive Heart Failure
  • Elderly or debilitated
  • Impaired liver function
  • Impaired kidney function
  • Dehydration
  • Fluid retention
  • GI bleed history/PUD
  • Asthma
  • Coagulopathy
  • Smoker
  • Corticosteriod use
  • Anticoagulant use
  • Alcohol use
  • Diuretic use
  • ACE Inhibitor use
  • Prolonged use


  • If symptoms labeled, (!), appear, stop usage immediately and contact your doctor.
  • Overdose is possible and deaths have occurred.
  • Do not take while on other pain medications.
  • Do not take while pregnant or breast feeding.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Diflunisal". A list of authors is available in Wikipedia.
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