[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Nonsteroidal anti-inflammatory drugs (NSAIDs)](https://durgical.com/en/pharmacology/classes/nonsteroidal-anti-inflammatory-drugs/) › Diflunisal

# 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.

Updated Nov 1, 2026

## Quick facts

**Group**
[Nonsteroidal anti-inflammatory drugs (NSAIDs)](https://durgical.com/en/pharmacology/classes/nonsteroidal-anti-inflammatory-drugs/)

**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.

On this page

- The basics Mechanism of action
- Indications
- Adverse effects
- Pharmacokinetics
- Memory aid

- Clinical What the labels mean

- Safety Contraindications
- Key interactions
- What is monitored
- Administration and safety
- Pregnancy and breastfeeding
- Nursing care

- Study Test yourself

- Connections Connections

## 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 →](https://durgical.com/en/conditions/knee-osteoarthritis/)
- Rheumatoid arthritis [Rheumatoid arthritis →](https://durgical.com/en/conditions/rheumatoid-arthritis/)

## Adverse effects

### Common

- Nausea, dyspepsia and abdominal pain
- Diarrhoea
- Headache, dizziness and drowsiness
- Rash and tinnitus

### Serious (rare, important)

- Heart attack and stroke (boxed warning of all NSAIDs)
- Bleeding, ulcer or perforation of the stomach or bowel, sometimes without warning
- Kidney injury and high potassium; worse heart failure and blood pressure
- Severe skin reactions and DRESS
- Possible link with Reye syndrome in children and teenagers, as a salicylate derivative

## 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

## Memory aid

Diflunisal: «DI-FLUoro salicylate that never becomes salicylate» – long-acting; raises paracetamol.

## 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.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/diflunisal/)

[More Pharmacology questions →](https://durgical.com/en/practice/?f=pharmacology)

## What the labels mean

**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…

## Connections

## Related drugs 4

- [Acetylsalicylic acid](https://durgical.com/en/pharmacology/acetylsalicylic-acid/)
- [Sulindac](https://durgical.com/en/pharmacology/sulindac/)
- [Indometacin](https://durgical.com/en/pharmacology/indometacin/)
- [Paracetamol](https://durgical.com/en/pharmacology/paracetamol/)

## Related conditions 2

- [Knee Osteoarthritis](https://durgical.com/en/conditions/knee-osteoarthritis/)
- [Rheumatoid arthritis](https://durgical.com/en/conditions/rheumatoid-arthritis/)

[← Back to the class: Nonsteroidal anti-inflammatory drugs (NSAIDs)](https://durgical.com/en/pharmacology/classes/nonsteroidal-anti-inflammatory-drugs/)

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](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=2043bab8-87c9-45ce-88c7-383f0d4c4b64) (DailyMed (U.S. National Library of Medicine), 2026); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=N02BA11) (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/pharmacology/diflunisal/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/diflunisal/