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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 * Treatment of mild to moderate pain. * Treatment of primary dysmenorrhea. * *Note:* Use is generally limited to short-term therapy (not exceeding 7 days). ## Adult Dosing * **Pain/Dysmenorrhea:** 500 mg orally as an initial dose, followed by 250 mg every 6 hours as needed. * **Maximum Duration:** 7 days. * **Maximum Dose:** 1,500 mg/day total dose. ## Pediatric Dosing * **Adolescents (≥14 years):** Same as adult dosing. * **Children (<14 years):** Safety and efficacy have not been established. Use is generally not recommended. ## Dose Adjustments * **Renal Impairment:** Contraindicated in patients with severe renal impairment. Use with extreme caution and monitor closely in mild-to-moderate impairment. * **Hepatic Impairment:** Use with caution; monitor for increased risk of adverse effects. Consider dose reduction. * **Geriatric Patients:** Use the lowest effective dose for the shortest duration due to increased risk of gastrointestinal (GI) and cardiovascular toxicity. ## Contraindications * Hypersensitivity to mefenamic acid, aspirin, or other NSAIDs. * 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 GI ulceration or inflammatory bowel disease (IBD). * Severe renal or hepatic impairment. ## Adverse Effects * **Common:** GI distress (nausea, diarrhea, abdominal pain), dizziness, headache. * **Serious:** GI bleeding, ulceration, perforation (can occur at any time without warning), cardiovascular thrombotic events (myocardial infarction, stroke), hypertension, fluid retention, renal impairment, and severe skin reactions (e.g., Stevens-Johnson Syndrome). ## Key Drug Interactions * **Anticoagulants/Antiplatelets (e.g., Warfarin):** Increased risk of bleeding. * **ACE Inhibitors/ARBs/Diuretics:** Reduced antihypertensive effect and increased risk of acute kidney injury. * **Methotrexate:** Increased risk of toxicity due to decreased clearance. * **Lithium:** Potential for increased plasma concentrations and lithium toxicity. * **Other NSAIDs/Corticosteroids:** Increased risk of GI toxicity. ## Monitoring * **Baseline/Routine:** Periodic renal function tests, CBC (if on long-term therapy), and monitoring for signs of GI bleeding (e.g., dark stools, epigastric pain). * **Blood Pressure:** Regular monitoring, especially in patients with hypertension. ## Clinical Pearls * **Administration:** Should be taken with food or milk to minimize GI irritation. * **Cardiovascular Warning:** Like all NSAIDs, mefenamic acid is associated with an increased risk of serious cardiovascular thrombotic events. * **Diarrhea:** Diarrhea is a notably common side effect of mefenamic acid that may be dose-related and requires discontinuation if severe. * **Duration:** Due to the risk of hemolytic anemia and hepatotoxicity with prolonged use, it is not recommended for chronic pain conditions. *** *Disclaimer: This information is for educational purposes only. Dosing, contraindications, and drug interactions can change or be subject to specific local institutional protocols. Always verify current prescribing information via official manufacturer labeling (e.g., FDA-approved package inserts) or clinical decision support tools before prescribing or administering medication.*