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# Mefenamic Acid ## Overview Mefenamic acid is an anthranilic acid derivative nonsteroidal anti-inflammatory drug (NSAID). It exhibits analgesic, anti-inflammatory, and antipyretic properties via the inhibition of cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis. ## Primary Indications * Treatment of mild to moderate pain. * Primary dysmenorrhea. * *Note:* Due to potential for serious gastrointestinal and renal toxicity, therapy should be limited to short-term use (typically ≤ 7 days). ## Adult Dosing * **Pain/Dysmenorrhea:** 500 mg initially, followed by 250 mg every 6 hours as needed. * **Maximum Dose:** Do not exceed 1,500 mg per 24 hours. ## Pediatric Dosing * **Children ≥ 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 avoided. ## Dose Adjustments * **Renal Impairment:** Avoid in severe renal impairment (CrCl < 30 mL/min). Use with caution and dose reduction in mild-to-moderate impairment. * **Hepatic Impairment:** Use with extreme caution; avoid in patients with active liver disease or significantly elevated LFTs. ## Contraindications * Known hypersensitivity (including asthma, urticaria, or allergic-type reactions) to aspirin or other NSAIDs. * History of GI bleeding or perforation related to NSAID therapy. * Active peptic ulcer disease or inflammatory bowel disease. * Coronary artery bypass graft (CABG) surgery (perioperative pain management). * Severe renal or hepatic failure. * Third trimester of pregnancy (risk of premature closure of the ductus arteriosus). ## Adverse Effects * **Gastrointestinal:** Abdominal pain, diarrhea (common, can be severe), nausea, dyspepsia, risk of peptic ulceration/GI bleed. * **Neurological:** Headache, dizziness, nervousness. * **Renal/Cardiovascular:** Fluid retention, edema, hypertension, elevated serum creatinine, potential increased risk of CV thrombotic events. * **Hematologic:** Anemia, rare blood dyscrasias. ## Key Drug Interactions * **Anticoagulants (e.g., Warfarin):** Increased risk of bleeding. * **Antiplatelet Agents (e.g., Clopidogrel, Aspirin):** Increased risk of GI toxicity/bleeding. * **ACE Inhibitors/ARBs/Diuretics:** Reduced antihypertensive efficacy and increased risk of acute renal failure. * **Lithium/Methotrexate:** NSAIDs may decrease renal clearance, leading to potential toxicity. * **Selective Serotonin Reuptake Inhibitors (SSRIs):** Increased risk of GI bleeding. ## Monitoring * **Renal Function:** Monitor serum creatinine and BUN in high-risk patients. * **GI Health:** Monitor for signs/symptoms of GI ulceration or bleeding. * **Blood Pressure:** Regular monitoring, especially in patients with hypertension. * **CBC:** Periodic monitoring if long-term therapy is required (rarely indicated due to short-term use restriction). ## Clinical Pearls * **GI Toxicity:** Mefenamic acid is known to cause diarrhea more frequently than many other NSAIDs; if diarrhea occurs, the dose should be reduced or the drug discontinued. * **Duration:** Limit total duration of treatment to 7 days or less to minimize severe adverse outcomes. * **Administration:** Take with food or milk to minimize gastrointestinal upset. * **CV Risk:** Use the lowest effective dose for the shortest duration possible, as all NSAIDs carry a warning for increased risk of serious cardiovascular thrombotic events. *** **Educational Disclaimer:** This information is for educational purposes only. Clinical practice protocols vary by institution and region. Always verify specific dosages, contraindications, and drug interactions against current, authoritative clinical resources (e.g., Lexicomp, UpToDate, or the manufacturer’s product label) before prescribing or administering medication.