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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. Its use is generally limited to short-term therapy due to the risk of serious adverse effects. ## Primary Indications * Treatment of mild to moderate pain. * Treatment of primary dysmenorrhea. ## Adult Dosing * **Pain/Dysmenorrhea:** 500 mg orally initially, followed by 250 mg every 6 hours as needed. * **Max Duration:** Limit therapy to no more than 7 days. ## Pediatric Dosing * **Children >14 years:** Use adult dosing (500 mg initial, 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 severe renal impairment (CrCl <30 mL/min). Use with caution in mild-to-moderate impairment; monitor renal function closely. * **Hepatic Impairment:** Use with caution; dose reduction may be required. Avoid in severe hepatic impairment. * **Geriatric:** Use the lowest effective dose for the shortest duration, as older adults are at higher risk for GI bleeding and renal complications. ## Contraindications * Hypersensitivity to mefenamic acid, aspirin, or other NSAIDs (risk of anaphylaxis/asthma). * History of asthma, urticaria, or allergic-type reactions to aspirin or other NSAIDs. * Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery. * Active peptic ulcer disease or GI bleeding. * Severe renal or hepatic impairment. ## Adverse Effects * **Common:** Abdominal pain, constipation, diarrhea, nausea, dyspepsia, dizziness, headache. * **Serious:** GI bleeding/perforation, myocardial infarction, stroke, peptic ulceration, renal failure, elevated liver enzymes, blood dyscrasias (e.g., hemolytic anemia), and skin reactions (e.g., Stevens-Johnson syndrome). ## Key Drug Interactions * **Anticoagulants (e.g., Warfarin):** Increased risk of major bleeding. * **Antiplatelets/SSRIs:** Increased risk of GI toxicity/bleeding. * **Antihypertensives (ACE inhibitors, ARBs, Beta-blockers, Diuretics):** Reduced antihypertensive efficacy and increased risk of renal impairment. * **Lithium/Methotrexate:** NSAIDs may decrease clearance, increasing risk of toxicity. * **Corticosteroids:** Increased risk of GI ulceration. ## Monitoring * **Renal:** Serum creatinine, BUN, and electrolytes, especially in elderly or those with chronic kidney disease. * **GI:** Monitor for signs of occult bleeding (e.g., dark tarry stools, anemia) or dyspepsia. * **Blood Pressure:** Monitor periodically, as NSAIDs can increase BP. * **Liver:** Periodic LFTs if long-term use is (rarely) clinically indicated. ## Clinical Pearls * **GI Protection:** Administer with food or milk to minimize gastrointestinal irritation. * **Cardiovascular Risk:** All NSAIDs carry a black box warning for increased risk of serious cardiovascular thrombotic events (myocardial infarction and stroke). * **Dysmenorrhea:** Evidence suggests NSAIDs are most effective when started at the onset of menses or pain. * **Diarrhea:** Mefenamic acid is specifically noted to cause diarrhea more frequently than other NSAIDs; this is often dose-related and may require discontinuation of the drug. *** **Educational Disclaimer:** This information is for educational purposes only and does not constitute medical advice. Always verify current prescribing information, local clinical protocols, and manufacturer labels before administering any medication. Consult with a licensed pharmacist or physician for specific clinical decisions.