Diflunisal
NSAIDs
Nonsteroidal anti-inflammatory drugs (NSAIDs)Pregnancy: avoid
Avoid from week 20: from about 20 weeks NSAIDs can reduce amniotic fluid through their effect on the fetal kidney, and from about 30 weeks they can close the fetal ductus…
A long-acting salicylic acid derivative NSAID for pain and arthritis. Unlike aspirin it is not turned into salicylate; it raises paracetamol levels.
Quick facts
- Group
- Nonsteroidal anti-inflammatory drugs (NSAIDs)
- Target
- Cyclooxygenase 1 and 2 (COX-1/COX-2)
- Used for
- Mild to moderate pain · Osteoarthritis
- Key effects
- Nausea · Diarrhoea · Headache
- Monitor
- Blood pressure · Signs of gastrointestinal bleeding
- ATC
- N02BA11
No doses: the clinician sets them by the current guideline.
Mechanism of action
Diflunisal, a difluorophenyl derivative of salicylic acid, inhibits prostaglandin synthesis by cyclooxygenase in peripheral tissues. It is not metabolised to salicylic acid.
- Inhibits cyclooxygenase in peripheral tissues
- Fewer prostaglandins sensitise pain nerves
- Long, non-linear kinetics: steady state takes days
Indications
- Mild to moderate pain
- Osteoarthritis Knee Osteoarthritis →
- Rheumatoid arthritis Rheumatoid arthritis →
Adverse effects
Common
- Nausea, dyspepsia and abdominal pain
- Diarrhoea
- Headache, dizziness and drowsiness
- Rash and tinnitus
Contraindications
- Asthma, hives or allergic-type reactions after aspirin or another NSAID
- Pain around coronary artery bypass graft (CABG) surgery
- Hypersensitivity to diflunisal
Key interactions
- Paracetamol (acetaminophen)
- About 50% higher paracetamol levels; risk of liver toxicity
- Indometacin
- Fatal gastrointestinal bleeding reported; not combined
- Warfarin
- Longer prothrombin time; close monitoring
- Antacids
- Lower diflunisal levels with regular use
What is monitored
- Blood pressure, swelling and signs of heart failure
- Signs of gastrointestinal bleeding (black stools, vomiting blood, anaemia)
- Kidney function, potassium, liver tests and blood count in long-term use
Administration and safety
- Given by mouth at the lowest effective dose for the shortest time
- Not given with indometacin or other NSAIDs
Pregnancy and breastfeeding
Avoid from week 20: from about 20 weeks NSAIDs can reduce amniotic fluid through their effect on the fetal kidney, and from about 30 weeks they can close the fetal ductus arteriosus too early.
Nursing care
- Ask about ulcers, bleeding, kidney or heart disease and aspirin-sensitive asthma before the first dose
- Check blood pressure and fluid status during treatment
- Teach to report black stools, vomiting blood, chest pain, weakness on one side or rash
- Teach to avoid taking another NSAID at the same time, including over-the-counter ones
Pharmacokinetics
- Absorption
- Rapid and nearly complete by mouth
- Distribution
- More than 99% bound to plasma proteins
- Elimination
- In the urine as glucuronide conjugates; kinetics are dose-dependent
- Half-life
- About 8 to 12 hours
Test yourself
Think of the answer, then tap the question to see it.
Is diflunisal converted to salicylic acid like aspirin?
No; it is excreted as glucuronides.
Which NSAID must not be combined with diflunisal, and why?
Indometacin, because fatal gastrointestinal bleeding has been reported.
What does diflunisal do to paracetamol levels?
It raises them by about half.
Connections
← Back to the class: Nonsteroidal anti-inflammatory drugs (NSAIDs)
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - DIFLUNISAL tablet, film coated (DailyMed (U.S. National Library of Medicine), 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
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Representative model, for educational purposes only.