mefenamic acid: clinical use

Prescribing considerations

• Assess gastrointestinal, cardiovascular, renal, hepatic, bleeding and hypersensitivity risks, including concurrent medicines and dehydration.
• Older people are more susceptible to gastrointestinal bleeding, perforation and renal adverse effects.
• Avoid concurrent NSAIDs. Consider gastroprotection and medicine alternatives according to individual risk assessment.
• Withdraw immediately if diarrhoea develops; continued use despite diarrhoea has been associated with proctocolitis.
• Failure to improve dysmenorrhoea or menorrhagia should prompt investigation for another cause.
• Mefenamic acid may impair female fertility; review use when conception is planned or infertility is being investigated.
• Use caution with asthma, epilepsy, systemic lupus erythematosus, hypertension, cardiovascular disease and known or suspected poor CYP2C9 metabolism.

Contraindications and cautions

• Hypersensitivity to mefenamic acid or formulation excipients.
• Previous asthma, bronchospasm, rhinitis, angioedema, urticaria or another hypersensitivity reaction caused by aspirin or another NSAID.
• Active or recurrent peptic ulcer or gastrointestinal haemorrhage, or previous NSAID-related gastrointestinal bleeding or perforation.
• Inflammatory bowel disease.
• Severe renal, hepatic or cardiac failure.
• Third trimester of pregnancy.
• Pain following coronary artery bypass graft surgery.

Monitoring

• Consider baseline blood pressure, renal function, full blood count and serum creatinine; consider liver tests where hepatic impairment is present.
• After initiation or treatment changes, consider renal function and full blood count, blood pressure, and haemoglobin when gastrointestinal risk is high.
• For continued treatment, periodically reassess blood pressure, renal function, full blood count, liver function where indicated, efficacy and adverse effects.
• During prolonged therapy, specifically watch for diarrhoea, rash, hepatic dysfunction and blood dyscrasias.
• After exposure for several days from week 20 of pregnancy, specialist antenatal monitoring for oligohydramnios and ductus arteriosus constriction may be indicated.

Clinical pharmacology

Mefenamic acid is a fenamate NSAID with analgesic, anti-inflammatory and antipyretic activity. It inhibits cyclo-oxygenase-mediated prostaglandin synthesis and may also reduce tissue responses to prostaglandins. Oral absorption occurs from the gastrointestinal tract, with metabolism involving CYP2C9.

Formulation and product differences

• Selected products include film-coated tablets, hard capsules and an oral suspension.
• The selected tablet and capsule formulations contain lactose; check excipients in people with relevant hereditary carbohydrate-intolerance disorders.
• The suspension contains sucrose, sorbitol, sodium benzoate, ethanol, propylene glycol and sodium, creating additional considerations for young children and people with hereditary fructose or related sugar-intolerance disorders.

Capsule

Route: Oral

Strengths: 250 mg

Oral suspension

Route: Oral

Strengths: 50 mg/5 mL

Tablet

Route: Oral

Strengths: 500 mg