[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/) › Mefenamic acid

# Mefenamic acid

## 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 fenamate NSAID for short-term pain and period pain (dysmenorrhoea). Use for pain is limited to one week; it carries all NSAID heart and gut warnings.

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**
Primary dysmenorrhoea

**Key effects**
Abdominal pain · Diarrhoea · Headache and dizziness

**Monitor**
Blood pressure · Signs of gastrointestinal bleeding

**ATC**
M01AG01

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

✂**Cyclooxygenase 1 and 2 (COX-1/COX-2)**Mefenamic acid

ⓘ The figure shows mefenamic acid itself in the active site of human COX-2.

**Target in 3D:** Cyclooxygenase 1 and 2 (COX-1/COX-2). PDB structure 5IKR (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/5IKR) · Drag to rotate · pinch to zoom

Mefenamic acid inhibits COX-1 and COX-2 and so lowers prostaglandin production. In the uterus, less prostaglandin means weaker, less painful contractions, which is why it is used for primary dysmenorrhoea.

- Blocks COX-1 and COX-2
- Less prostaglandin is made in tissue and uterus
- Less pain and weaker uterine cramps

## Indications

- Primary dysmenorrhoea [Dysmenorrhoea →](https://durgical.com/en/conditions/dysmenorrhoea/)
- Short-term mild to moderate pain (from 14 years, no more than one week)

## Adverse effects

### Common

- Abdominal pain, dyspepsia and heartburn
- Diarrhoea, nausea and vomiting
- Headache and dizziness
- 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
- Liver injury and anaemia

## Contraindications

- Asthma, hives or allergic-type reactions after aspirin or another NSAID
- Pain around coronary artery bypass graft (CABG) surgery
- Hypersensitivity to mefenamic acid

## Key interactions

**Warfarin, antiplatelets, SSRIs and SNRIs**
More bleeding, mainly in the gut

**ACE inhibitors, ARBs and diuretics**
Weaker blood-pressure and diuretic effect; risk of kidney injury

**Lithium and methotrexate**
Higher levels and toxicity of lithium or methotrexate

## 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
- For pain, treatment lasts no more than one week

## 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

**Metabolism**
By CYP2C9 to hydroxylated products, then glucuronidation

**Elimination**
About half in the urine, the rest largely in the faeces

**Half-life**
Short, about 2 hours

## Memory aid

Mefenamic acid: «MEnstrual FENamate» – period pain, one week at most.

## Test yourself

Think of the answer, then tap the question to see it.

## For which gynaecological pain is mefenamic acid used?

Primary dysmenorrhoea.

## What limit applies to its use for general pain?

No more than one week.

## Which CYP enzyme metabolises mefenamic acid?

CYP2C9.

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

[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

- [Ibuprofen](https://durgical.com/en/pharmacology/ibuprofen/)
- [Naproxen](https://durgical.com/en/pharmacology/naproxen/)
- [Diclofenac](https://durgical.com/en/pharmacology/diclofenac/)
- [Celecoxib](https://durgical.com/en/pharmacology/celecoxib/)

## Related conditions 1

- [Dysmenorrhoea](https://durgical.com/en/conditions/dysmenorrhoea/)

[← 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 - MEFENAMIC ACID capsule](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=d15733a9-d5fd-4d5f-86ce-e7ed8c706c7f) (DailyMed (U.S. National Library of Medicine), 2026); [5IKR: The Structure of Mefenamic Acid Bound to Human Cyclooxygenase-2](https://www.rcsb.org/structure/5IKR) (RCSB Protein Data Bank, 2016); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=M01AG01) (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

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Representative model, for educational purposes only.

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