Non-selective NSAID Pregnancy: Contraindicated during the last trimester of pregnancy (risk of closure of the ductus arteriosus). Should not be used during the first two trimesters or labour unless the potential benefit outweighs the potential risk to the foetus. From the 20th week of pregnancy onward may cause oligohydramnios from foetal renal dysfunction, and ductus arteriosus constriction has been reported after second-trimester treatment — consider antenatal monitoring after several days' exposure from week 20 and discontinue if either is found. Should not be taken by nursing mothers (trace amounts pass into breast milk). May impair female fertility — not recommended in women attempting to conceive.

Mefenamic acid

Brand names: Ponstan

A non-steroidal anti-inflammatory drug used for dysmenorrhoea, heavy menstrual bleeding, and mild to moderate pain.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: 500 mg (two 250 mg capsules)

Route: Oral — taken preferably with or after food

Frequency: Three times daily

Max: Do not exceed the stated dose (500 mg three times daily); use the lowest effective dose for the shortest duration necessary to control symptoms. No separate numeric ceiling is given in the UK SPC.

SPC §4.2 (Mefenamic Acid 250 mg Capsules). IN MENORRHAGIA: to be administered on the first day of excessive bleeding and continued according to the judgement of the physician. IN DYSMENORRHOEA: to be administered at the onset of menstrual pain and continued according to the judgement of the physician. ELDERLY (over 65 years): as for adults, but the elderly are at increased risk of the serious consequences of adverse reactions — use the lowest effective dose for the shortest possible duration and monitor regularly for GI bleeding; use with caution in elderly patients with dehydration and renal disease. Non-oliguric renal failure and proctocolitis have been reported mainly in elderly patients who did not discontinue mefenamic acid after developing diarrhoea — if diarrhoea develops, withdraw the drug immediately and do not re-challenge. PAEDIATRIC: the SPC states only that children under 12 years of age should be given Mefenamic Acid Suspension (50 mg/5 mL) — no numeric paediatric dose is given in this SPC; verify paediatric dosing against a children's formulary. US LABELLING (cross-check only — verify against UK SPC): for the relief of acute pain in adults and adolescents 14 years and older, 500 mg as an initial dose followed by 250 mg every 6 hours as needed, usually not to exceed one week; for primary dysmenorrhoea, 500 mg as an initial dose followed by 250 mg every 6 hours orally starting with the onset of bleeding and associated symptoms, usually not necessary for more than 2 to 3 days. INTERACTIONS below are taken from the US label (Table 2) — UK SPC §4.5 was not captured in this bundle.

Dose adjustments

Renal

Contraindicated in renal failure. No numeric dose adjustment is given in the SPC. NSAIDs may cause a dose-dependent reduction in prostaglandin formation and precipitate renal failure — greatest risk in impaired renal function, cardiac impairment, liver dysfunction, those taking diuretics and the elderly; monitor renal function in these patients and use with caution in patients with dehydration and renal disease.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to the active substance or any of the excipients
Inflammatory bowel disease
History of gastrointestinal bleeding or perforation related to previous NSAID therapy; active or history of recurrent peptic ulcer/haemorrhage (two or more distinct episodes of proven ulceration or bleeding)
Severe heart failure, hepatic failure and renal failure
Previous hypersensitivity reaction (e.g. asthma, bronchospasm, rhinitis, angioedema or urticaria) to aspirin, ibuprofen or other NSAIDs
During the last trimester of pregnancy
Treatment of pain after coronary artery bypass graft (CABG) surgery

Side effects

Diarrhoea (may occur soon after starting or after months of use; associated proctocolitis has been found — withdraw the drug immediately and do not re-administer)
Peptic ulcers, perforation or GI bleeding, sometimes fatal, particularly in the elderly
Haematological: haemolytic anaemia (reversible on stopping), anaemia, leukopenia, thrombocytopenia, agranulocytosis, aplastic anaemia, pancytopenia
Hypersensitivity reactions — non-specific allergic reactions and anaphylaxis; asthma, aggravated asthma, bronchospasm or dyspnoea; rashes, pruritus, urticaria, angioedema and rarely exfoliative or bullous dermatoses (including epidermal necrolysis and erythema multiforme)
Nervous system: headache, dizziness, drowsiness, paraesthesia, blurred vision, convulsions; aseptic meningitis (especially in patients with existing auto-immune disorders)
Cardiovascular: oedema, hypertension and cardiac failure; a small increased risk of arterial thrombotic events (e.g. myocardial infarction or stroke) with some NSAIDs at high doses/long-term use

Interactions

Anticoagulants (e.g. warfarin) — synergistic effect on bleeding; increased risk of serious bleeding (US label Table 2)
Antiplatelet agents (e.g. aspirin), SSRIs and SNRIs — increased bleeding risk; monitor for signs of bleeding (US label Table 2)
Aspirin — concomitant use gives no greater therapeutic effect but significantly increases the incidence of GI adverse reactions (US label Table 2)
Other NSAIDs including cyclo-oxygenase-2 specific inhibitors — concomitant use should be avoided (UK SPC §4.4)
Diuretics and other drugs that impair renal function — increased risk of precipitating renal failure, particularly in patients with impaired renal or cardiac function, liver dysfunction and the elderly (UK SPC §4.4)

Clinical monograph

How it works

It inhibits cyclo-oxygenase, reducing prostaglandin synthesis and thereby easing pain, inflammation and menstrual blood loss.

Prescribing in practice

As with other NSAIDs it carries gastrointestinal bleeding, cardiovascular and renal risks; use the lowest effective dose for the shortest time and consider gastroprotection in at-risk patients.
Overdose can provoke convulsions, so counsel against exceeding the recommended dose.
Avoid in active peptic ulceration, severe heart failure, significant renal impairment, and in the third trimester of pregnancy.

Monitoring

Monitor for gastrointestinal symptoms, blood pressure and renal function in those with risk factors or on prolonged treatment.

Counselling the patient

Take with or after food to reduce stomach upset.
Stop and seek advice if you have black stools, vomit blood, or develop severe indigestion.
It is most effective for period pain and heavy bleeding when started as symptoms begin.

Evidence & guidelines

NICE guidance on heavy menstrual bleeding (NG88) lists NSAIDs such as mefenamic acid among pharmacological options, particularly where dysmenorrhoea coexists.

Reference: NICE NG88; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

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