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# Mefenamic Acid ## Overview Mefenamic acid is an anthranilic acid derivative nonsteroidal anti-inflammatory drug (NSAID) that exhibits analgesic, anti-inflammatory, and antipyretic properties. Like other NSAIDs, it inhibits cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis. ## 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. * **Duration:** Therapy should not exceed 7 days duration due to risk of serious gastrointestinal and renal adverse effects. ## Pediatric Dosing * **Adolescents (≥14 years):** Same as 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 and monitor carefully in mild-to-moderate impairment. * **Hepatic Impairment:** Clearance may be impaired; use with extreme caution or avoid. * **Elderly:** Use the lowest effective dose for the shortest duration possible, as elderly patients are at higher risk for NSAID-related gastrointestinal bleeding and renal failure. ## Contraindications * Known hypersensitivity to mefenamic acid or aspirin/other NSAIDs. * History of asthma, urticaria, or allergic-type reactions after taking aspirin or other NSAIDs. * Active peptic ulcer disease or gastrointestinal bleeding. * History of recent coronary artery bypass graft (CABG) surgery (perioperative pain management). * Severe renal or hepatic failure. ## Adverse Effects * **Common:** Nausea, vomiting, diarrhea, abdominal pain, dyspepsia, dizziness, headache. * **Serious:** Gastrointestinal ulceration/perforation, gastrointestinal bleeding, myocardial infarction, stroke, renal insufficiency, fluid retention/edema, hepatotoxicity, and blood dyscrasias (e.g., hemolytic anemia). ## Key Drug Interactions * **Anticoagulants (e.g., Warfarin):** Increased risk of bleeding. * **Antiplatelet agents/SSRIs:** Increased risk of GI bleeding. * **Antihypertensives (ACE inhibitors, ARBs, Beta-blockers, Diuretics):** May diminish the antihypertensive effect; risk of renal impairment increased especially with diuretics. * **Lithium/Methotrexate:** NSAIDs may decrease clearance, increasing serum concentrations and toxicity. ## Monitoring * **Baseline/Intermittent:** CBC, chemistry panel (renal function, liver enzymes). * **Clinical:** Monitor for signs of gastrointestinal bleeding (occult blood, anemia), edema, and changes in blood pressure. ## Clinical Pearls * **GI Protection:** Consider H2 blockers or proton pump inhibitors in high-risk patients, though this does not eliminate risk entirely. * **Administration:** Take with food or milk to minimize gastrointestinal upset. * **Cardiovascular Risk:** Like all non-aspirin NSAIDs, mefenamic acid is associated with an increased risk of serious cardiovascular thrombotic events. * **Limit Therapy:** The strict 7-day limit is recommended due to the potential for severe diarrhea and autoimmune-type hemolytic anemia associated with prolonged use. *** *Disclaimer: This information is for educational purposes only. Always consult current clinical practice guidelines, hospital-specific protocols, and package inserts before prescribing or administering medication.*