Recommended Dose for Mefenamic Acid
For adults, mefenamic acid is dosed at 500 mg orally every 8 hours (three times daily) for a maximum of 3-5 days, particularly for primary dysmenorrhea and acute pain. 1, 2
Standard Adult Dosing
- Initial dose: 500 mg orally, followed by 250 mg every 6 hours as needed 3
- Alternative regimen: 500 mg every 8 hours (three times daily) for dysmenorrhea 1, 2
- Maximum duration: Treatment should not exceed 7 days for acute conditions 3
- Timing for dysmenorrhea: Begin dosing one day before expected menstruation and continue for 3-5 days 1, 2
Clinical Efficacy Data
- A single 500 mg dose provides effective relief for moderate to severe acute postoperative pain, with a number needed to treat (NNT) of 4.0 for at least 50% pain relief over 6 hours 3
- For primary dysmenorrhea, 500 mg every 8 hours produces complete symptom relief in approximately 88.6% of patients 1
- The 250 mg dose has insufficient evidence for efficacy assessment in acute pain settings 3
Contraindications and Precautions
- Avoid in older adults: Mefenamic acid appears on the American Geriatrics Society Beers Criteria as potentially inappropriate for use in adults ≥65 years due to increased risk of gastrointestinal bleeding, peptic ulcer disease, and acute kidney injury 4
- High-risk populations: Use extreme caution or avoid in patients with history of peptic ulcer disease, those taking anticoagulants or antiplatelet agents, or patients with heart failure 4
- Gastrointestinal protection: Consider concomitant proton pump inhibitor or misoprostol in high-risk patients (age >75 years, history of GI bleeding, concurrent use of anticoagulants, corticosteroids, or SSRIs) 4
- Renal considerations: NSAIDs including mefenamic acid increase risk of acute kidney injury and should be used cautiously in patients with renal impairment 4
Common Pitfalls to Avoid
- Do not exceed 7 days of treatment for acute conditions, as mefenamic acid is intended for short-term use only 3
- Do not use lower doses (250 mg) as monotherapy for moderate to severe pain, as efficacy data are insufficient 3
- Monitor for gastrointestinal adverse effects, particularly in patients not receiving gastroprotection 4
- Avoid combining with other NSAIDs, as this significantly increases risk of adverse effects without additional benefit 4