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# Mefenamic Acid ## Overview Mefenamic acid is an anthranilic acid derivative nonsteroidal anti-inflammatory drug (NSAID) that inhibits cyclooxygenase (COX-1 and COX-2) enzymes. It possesses analgesic, anti-inflammatory, and antipyretic properties. ## Primary Indications * Treatment of mild to moderate pain. * Treatment of primary dysmenorrhea. * *Note:* Therapy should be limited to $\leq$ 7 days. ## Adult Dosing * **Initial Dose:** 500 mg orally, followed by 250 mg every 6 hours as needed. * **Maximum Dose:** Do not exceed 1,500 mg per day. ## Pediatric Dosing * **Children $\geq$ 14 years:** Use adult dosing (500 mg initially, then 250 mg every 6 hours). * **Children < 14 years:** Safety and efficacy have not been established; use is generally not recommended. ## Dose Adjustments * **Renal Impairment:** Avoid in patients with severe renal impairment (CrCl < 30 mL/min). Use with caution in mild-to-moderate impairment; monitor renal function closely. * **Hepatic Impairment:** Use with caution; monitor for increased risk of adverse effects. ## Contraindications * Known hypersensitivity (e.g., urticaria, asthma) to mefenamic acid, aspirin, or other NSAIDs. * History of asthma precipitated by aspirin or other NSAIDs. * Active peptic ulcer disease or gastrointestinal (GI) bleeding. * History of inflammatory bowel disease (IBD). * Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery. * Severe renal or hepatic impairment. ## Adverse Effects * **GI:** Abdominal pain, diarrhea (common and may be dose-limiting), nausea, dyspepsia, risk of GI ulceration or perforation. * **Renal:** Fluid retention, edema, risk of acute kidney injury. * **Cardiovascular:** Increased risk of myocardial infarction, stroke, and hypertension. * **Hematologic:** Anemia, blood dyscrasias (rare cases of autoimmune hemolytic anemia with long-term use). * **CNS:** Dizziness, headache, drowsiness. ## Key Drug Interactions * **Anticoagulants (e.g., Warfarin):** Increased risk of bleeding; monitor INR. * **Antiplatelets/SSRIs:** Increased risk of GI bleeding. * **Antihypertensives (ACE inhibitors, Diuretics):** Reduced efficacy and risk of renal impairment. * **Lithium/Methotrexate:** NSAIDs may decrease clearance, increasing risk of toxicity. * **Other NSAIDs/Corticosteroids:** Increased risk of GI toxicity and bleeding. ## Monitoring * Baseline and periodic CBC (if prolonged use). * Renal function (BUN/SCr) and electrolytes, especially in the elderly. * Blood pressure monitoring. * Stool occult blood if signs of GI distress occur. ## Clinical Pearls * **Duration Limit:** Due to the risk of significant GI toxicity and hemolytic anemia, therapy should not exceed 7 days. * **Administration:** Administer with food or milk to minimize GI irritation. * **Warning:** Like all NSAIDs, mefenamic acid carries a boxed warning regarding serious cardiovascular thrombotic events and serious gastrointestinal adverse events. * **Diarrhea:** This specific NSAID is uniquely associated with diarrhea; if developed, therapy should be discontinued. *** **Educational Disclaimer:** This information is for educational purposes only. Drug dosing, contraindications, and interactions can change. Always consult the most current official prescribing information (FDA labels or equivalent regulatory documents) and institutional clinical guidelines before prescribing or administering medication.