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# Mefenamic Acid ## Overview Mefenamic acid is a nonsteroidal anti-inflammatory drug (NSAID) of the fenamate class. It acts by inhibiting the cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis. Its pharmacological use is limited by a relatively high risk of gastrointestinal and hematologic toxicity compared to other NSAIDs. ## Primary Indications * Treatment of mild to moderate pain. * Treatment of primary dysmenorrhea. * *Note:* Use is generally limited to short-term therapy (maximum 7 days). ## Adult Dosing * **Pain/Dysmenorrhea:** 500 mg initially, followed by 250 mg every 6 hours as needed. * **Maximum Dose:** 1,500 mg per 24 hours. Limit duration of therapy to 7 days. ## Pediatric Dosing * **Ages 14 years and older:** Same as adult dosing. * **Under 14 years:** Safety and efficacy have not been established. Use is generally not recommended in this population. ## Dose Adjustments * **Renal Impairment:** Avoid in patients with severe renal impairment (CrCl <30 mL/min). Use with caution in mild-to-moderate impairment; adjust dose downward and monitor closely. * **Hepatic Impairment:** Avoid in severe hepatic impairment. Reduce dose in patients with mild-to-moderate liver disease. ## Contraindications * Known hypersensitivity (including aspirin-induced asthma or urticaria). * History of GI bleeding or perforation related to previous NSAID therapy. * Active peptic ulcer disease or inflammatory bowel disease. * Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery. * Severe heart failure or severe renal/hepatic impairment. ## Adverse Effects * **Gastrointestinal:** Diarrhea (frequent), abdominal pain, nausea, dyspepsia, risk of GI ulceration/bleeding. * **Hematologic:** Anemia, leukopenia, thrombocytopenia, hemolytic anemia (long-term use). * **Renal:** Fluid retention, edema, acute renal failure. * **Neurologic:** Dizziness, headache, drowsiness. ## Key Drug Interactions * **Anticoagulants/Antiplatelets (e.g., Warfarin, Heparin):** Increased risk of bleeding. * **ACE Inhibitors/ARBs/Diuretics:** Reduced antihypertensive effect and increased risk of acute kidney injury. * **Corticosteroids/SSRIs:** Increased risk of gastrointestinal ulceration. * **Methotrexate/Lithium:** Reduced renal clearance of these drugs, increasing toxicity risk. ## Monitoring * **Baseline/Intermittent:** Serum creatinine, BUN, and electrolytes. * **Monitoring:** Periodic CBC (if long-term/chronic use is considered), blood pressure monitoring, and signs/symptoms of GI bleeding or fluid retention. ## Clinical Pearls * **GI Caution:** Mefenamic acid is noted for causing diarrhea more frequently than many other NSAIDs; if diarrhea occurs, discontinue therapy immediately. * **Short-term Use:** Due to the risk of severe hemolytic anemia and hepatotoxicity, do not exceed the 7-day treatment recommendation. * **Administration:** Take with food or milk to minimize gastrointestinal discomfort. * **Black Box Warning:** All NSAIDs carry an increased risk of serious cardiovascular thrombotic events and serious gastrointestinal adverse events. *** *Disclaimer: This information is for educational purposes only. Clinical practices vary by institution and region. Always consult current, full prescribing information (FDA labels or equivalent regulatory documents) and local protocols before prescribing or administering medication.*