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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 by inhibiting cyclooxygenase (COX-1 and COX-2) enzymes, thereby reducing prostaglandin synthesis. ## Primary Indications * Management of mild to moderate pain. * Treatment of primary dysmenorrhea. * Duration of therapy should not exceed 7 days. ## Adult Dosing * **Initial Dose:** 500 mg orally. * **Maintenance Dose:** 250 mg orally every 6 hours as needed. * **Maximum Daily Dose:** 1500 mg/day (limited to 7 days of treatment). ## 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 for fluid retention and electrolyte disturbances. * **Hepatic Impairment:** Use with caution; monitor for hepatotoxicity. Avoid in severe hepatic impairment. * **Geriatric:** Initiate at the lowest effective dose due to increased risk of gastrointestinal (GI) bleeding and cardiovascular events. ## Contraindications * Known hypersensitivity (including aspirin or other NSAID-induced asthma/urticaria). * History of GI bleeding or perforation related to previous NSAID therapy. * Active peptic ulcer disease or inflammatory bowel disease. * Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery. * Severe heart failure. * Severe renal or hepatic impairment. ## Adverse Effects * **Common:** Diarrhea (most frequent), nausea, abdominal pain, constipation, dizziness, headache. * **Serious:** GI ulceration/bleeding, myocardial infarction, stroke, renal insufficiency, fluid retention/edema, hepatotoxicity, blood dyscrasias, and hypersensitivity reactions (anaphylaxis). ## Key Drug Interactions * **Anticoagulants (e.g., Warfarin):** Increased risk of bleeding. * **Antiplatelet Agents/SSRIs:** Increased risk of GI bleeding. * **Antihypertensives (ACE inhibitors, Beta-blockers, Diuretics):** Reduced antihypertensive effect; potential for renal failure. * **Lithium/Methotrexate:** Decreased renal clearance, leading to increased plasma concentrations and potential toxicity. ## Monitoring * **GI:** Monitor for signs of occult blood loss or dyspepsia. * **Renal/Hepatic:** Periodic monitoring of serum creatinine, BUN, and liver enzymes in long-term therapy (though rarely indicated given the 7-day restriction). * **Cardiovascular:** Monitor blood pressure and signs of fluid retention. ## Clinical Pearls * **Administration:** Administer with food or milk to minimize GI irritation. * **Duration:** Therapy is strictly limited to 7 days due to an increased risk of severe, sometimes fatal, GI and renal adverse effects associated with long-term use. * **Diarrhea:** Diarrhea is a dose-related side effect; if it occurs, the dose should be reduced or the drug discontinued. * **NSAID Class Effect:** All NSAIDs carry a boxed warning regarding serious cardiovascular thrombotic events and serious gastrointestinal adverse events. *** *Disclaimer: This information is for educational purposes and does not replace professional medical judgment. Always verify current prescribing information, institutional protocols, and patient-specific factors before prescribing or administering medication.*