Overview
Mefenamic acid is a nonsteroidal anti-inflammatory drug (NSAID) used for short-term relief of mild to moderate pain, including primary dysmenorrhea. It works by inhibiting prostaglandin synthesis, reducing inflammation and pain. It carries typical NSAID risks including gastrointestinal, cardiovascular, and renal adverse effects.
Mechanism of Action
Mefenamic acid inhibits cyclooxygenase (COX) enzymes, reducing prostaglandin synthesis. This decreases inflammation, pain, and fever by blocking the conversion of arachidonic acid to prostaglandin precursors.
Indications
- Short-term relief of mild to moderate pain
- Treatment of primary dysmenorrhea
Common Doses
- 250 mg capsules
- 500 mg capsules
Dosage
For pain: 500 mg initially, then 250 mg every 6 hours as needed. For dysmenorrhea: 500 mg initially, then 250 mg every 6 hours, starting at onset of menses. Maximum daily dose: 1,250 mg. Use shortest effective duration.
Contraindications
- Known hypersensitivity to mefenamic acid or any components
- History of asthma, urticaria, or allergic reactions to aspirin or other NSAIDs
- In the setting of coronary artery bypass graft (CABG) surgery
Side Effects
- Gastrointestinal: abdominal pain, constipation, diarrhea, dyspepsia, nausea, vomiting, GI ulcers, bleeding
- Cardiovascular: edema, hypertension, congestive heart failure
- Renal: abnormal renal function, renal failure
- Hepatic: elevated liver enzymes, hepatitis
- Dermatologic: pruritus, rashes, photosensitivity
- Central nervous system: dizziness, headache, drowsiness
- Hematologic: anemia, increased bleeding time
- Auditory: tinnitus
Interactions
- Anticoagulants (warfarin): increased bleeding risk
- Aspirin: increased GI toxicity without added benefit
- ACE inhibitors/ARBs/beta-blockers: diminished antihypertensive effect
- Diuretics: reduced natriuretic effect
- Lithium: increased lithium levels
- Methotrexate: increased toxicity risk
- Cyclosporine: increased nephrotoxicity
- Other NSAIDs/salicylates: increased GI toxicity
- Pemetrexed: increased toxicity risk
- Antacids with magnesium hydroxide: increased absorption
Counseling Points
- Take with food or milk to reduce GI upset
- Use shortest duration possible at lowest effective dose
- Report signs of GI bleeding (black/tarry stools, vomiting blood)
- Monitor for cardiovascular symptoms (chest pain, shortness of breath)
- Avoid alcohol consumption
- Report skin rash or allergic reactions immediately
- Do not take with other NSAIDs or aspirin unless directed
- Inform healthcare provider of all medications including OTC products