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# Mefenamic Acid ## Overview Mefenamic acid is a nonsteroidal anti-inflammatory drug (NSAID) of the fenamate class. It acts by inhibiting cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis. Its use is limited to short-term therapy (generally ≤7 days). ## Primary Indications * Treatment of mild to moderate pain. * Primary dysmenorrhea. ## Adult Dosing * **Standard dose:** 500 mg initially, followed by 250 mg every 6 hours as needed. * **Maximum duration:** Not to exceed 7 days of therapy. ## Pediatric Dosing * **Children 14 years and older:** 500 mg initially, followed by 250 mg every 6 hours as needed. * **Children under 14 years:** Safety and efficacy have not been established; use is generally avoided. ## Dose Adjustments * **Renal Impairment:** Avoid in patients with severe renal impairment (CrCl <30 mL/min). Use with caution and monitor closely in mild to moderate impairment. * **Hepatic Impairment:** Reduce dose in patients with hepatic impairment; monitor for toxicity. ## Contraindications * 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. * Active peptic ulcer disease or history of gastrointestinal (GI) bleeding. * Severe renal or hepatic failure. * Third trimester of pregnancy. ## Adverse Effects * **GI:** Diarrhea (common and sometimes severe), nausea, abdominal pain, GI ulceration/bleeding. * **Renal:** Fluid retention, edema, acute renal failure. * **CV:** Increased risk of thrombotic events, hypertension. * **Hematologic:** Anemia, blood dyscrasias (rare). * **CNS:** Dizziness, headache, drowsiness. ## Key Drug Interactions * **Anticoagulants (e.g., Warfarin):** Increased risk of bleeding due to antiplatelet effects and gastric mucosal injury. * **Anti-hypertensives:** NSAIDs may diminish the antihypertensive effect of ACE inhibitors, ARBs, and diuretics. * **Lithium/Methotrexate:** NSAIDs may decrease renal clearance, increasing risk of toxicity. * **Other NSAIDs/Corticosteroids:** Increased risk of GI toxicity and ulceration. ## Monitoring * **Baseline:** Renal function (BUN/SCr) and LFTs if long-term or high-risk. * **Ongoing:** Monitor for signs of GI bleeding, changes in blood pressure, and peripheral edema. Monitor Hb/Hct if chronic use occurs (not recommended). ## Clinical Pearls * **Diarrhea:** Mefenamic acid is uniquely associated with diarrhea, which can be severe; discontinue if diarrhea occurs. * **Duration:** Strict adherence to the 7-day limit is imperative due to the increased risk of GI and renal adverse events with prolonged use. * **Administration:** Administer with food to minimize GI upset. * **NSAID Class Effect:** All NSAIDs carry a boxed warning for increased risk of serious cardiovascular thrombotic events and serious gastrointestinal adverse events. *** *Educational Disclaimer: This information is for educational purposes only and does not constitute medical advice. Always consult the latest prescribing information (USPI/SmPC) and institutional clinical protocols before prescribing or administering medication.*