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# Mefenamic acid ## Overview Mefenamic acid is an anthranilic acid derivative nonsteroidal anti-inflammatory drug (NSAID). It exerts anti-inflammatory, analgesic, and antipyretic effects primarily through the inhibition of cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis. ## Primary Indications * Treatment of mild-to-moderate pain. * Primary dysmenorrhea (common clinical use). * *Note: Treatment duration should not exceed 7 days.* ## Adult Dosing * **Initial:** 500 mg orally once. * **Maintenance:** 250 mg orally every 6 hours as needed. * **Maximum:** 1,500 mg per day. ## Pediatric Dosing * **Children ≥ 14 years:** Same as adult dosing. * **Children < 14 years:** Safety and efficacy have not been established. Use is generally not recommended. ## Dose Adjustments * **Renal Impairment:** Avoid in severe renal impairment (CrCl < 30 mL/min). Use with caution in mild-to-moderate impairment. * **Hepatic Impairment:** Use with caution; dose reduction may be required. Avoid in severe hepatic impairment. * **Elderly:** Use the lowest effective dose for the shortest duration due to increased risk of gastrointestinal and cardiovascular adverse events. ## Contraindications * Hypersensitivity to mefenamic acid, aspirin, or other NSAIDs. * History of asthma, urticaria, or allergic-type reactions after taking aspirin or other NSAIDs. * Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery. * History of gastrointestinal (GI) bleeding or perforation related to previous NSAID therapy. * Active peptic ulcer disease or inflammatory bowel disease. ## Adverse Effects * **GI:** Diarrhea (common and sometimes dose-limiting), nausea, abdominal pain, GI ulceration, bleeding. * **Cardiovascular:** Hypertension, fluid retention, edema, increased risk of myocardial infarction and stroke. * **Renal:** Acute kidney injury, interstitial nephritis, hyperkalemia. * **Hematologic:** Anemia, thrombocytopenia (rare). ## Key Drug Interactions * **Anticoagulants (e.g., Warfarin):** Increased risk of major bleeding. * **Antiplatelets (e.g., Clopidogrel, Aspirin):** Increased GI toxicity/bleeding risk. * **ACE Inhibitors/ARBs/Diuretics:** Reduced antihypertensive efficacy; increased risk of acute renal failure. * **Lithium/Methotrexate:** Decreased renal clearance, leading to potential toxicity. ## Monitoring * **Renal Function:** Serum creatinine and electrolytes (especially in patients with baseline renal/cardiac disease). * **GI:** Monitor for signs of occult blood loss or anemia. * **Blood Pressure:** Regular monitoring in patients with hypertension. * **Symptoms:** Monitor for edema, rash, or signs of liver injury. ## Clinical Pearls * **GI Sensitivity:** Mefenamic acid is notorious for causing dose-dependent diarrhea; if it occurs, the dosage should be reduced or the drug discontinued. * **Duration:** Due to the risk of severe adverse effects (GI, renal, CV), it is historically labeled for short-term use (≤ 7 days). * **Administration:** Take with food or milk to minimize GI irritation. * **Cross-reactivity:** Patients sensitive to one NSAID often exhibit cross-sensitivity to others; exercise extreme caution. *** **Disclaimer:** This information is for educational purposes only. Clinical practice guidelines and drug labeling may vary by region. Always consult the most current official prescribing information (package insert) and institutional protocols before prescribing or administering any medication.