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# Mefenamic Acid ## Overview Mefenamic acid is an anthranilic acid derivative nonsteroidal anti-inflammatory drug (NSAID). It exerts analgesic, anti-inflammatory, and antipyretic effects primarily through the non-selective inhibition of cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis. ## Primary Indications * Treatment of mild to moderate pain. * Primary dysmenorrhea. * Note: Use is generally limited to short-term therapy (not exceeding 7 days). ## Adult Dosing * **Acute Pain/Dysmenorrhea:** 500 mg orally initially, followed by 250 mg every 6 hours as needed. * **Maximum Dose:** 1,500 mg per 24 hours. ## Pediatric Dosing * **Children ≥14 years:** Follow adult dosing guidelines. * **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 in mild-to-moderate impairment; monitor closely. * **Hepatic Impairment:** Use with caution. Consider lower doses, as NSAIDs can impact hepatic function and may be contraindicated in severe liver disease. ## Contraindications * Known hypersensitivity to mefenamic acid or aspirin/other NSAIDs. * History of asthma, urticaria, or allergic-type reactions after taking aspirin or other NSAIDs. * Treatment of perioperative pain in the setting of coronary artery bypass graft (CABG) surgery. * Active peptic ulceration or inflammatory bowel disease. * Severe renal or hepatic impairment. ## Adverse Effects * **Gastrointestinal:** Abdominal pain, nausea, diarrhea (common), dyspepsia, GI ulceration/bleeding. * **Renal:** Fluid retention, edema, acute renal failure, interstitial nephritis. * **Cardiovascular:** Hypertension, increased risk of serious thrombotic events (MI, stroke). * **Hematologic:** Anemia, leukopenia, thrombocytopenia (rare, usually with prolonged use). ## Key Drug Interactions * **Anticoagulants (e.g., Warfarin):** Increased risk of bleeding; monitor INR closely. * **Antiplatelet agents/SSRIs:** Increased risk of GI bleeding. * **ACE Inhibitors/ARBs/Diuretics:** Reduced antihypertensive efficacy and increased risk of renal impairment (nephrotoxicity). * **Lithium/Methotrexate:** Decreased renal clearance, leading to potential toxicity; monitor serum levels. ## Monitoring * **Renal Function:** Periodic BUN/Creatinine in long-term or high-risk patients. * **GI:** Monitor for signs of occult blood loss or evidence of ulceration (anemia, melena). * **Blood Pressure:** Monitor regularly during initiation and dose changes. * **CBC:** Periodic monitoring if used for prolonged durations (rarely exceeding 7 days). ## Clinical Pearls * **Duration Limit:** Mefenamic acid is indicated for short-term use only (maximum 7 consecutive days). * **Administration:** Take with food or milk to minimize gastrointestinal irritation. * **Cardiovascular Warning:** Like all NSAIDs, it carries a boxed warning for increased risk of serious cardiovascular thrombotic events and gastrointestinal toxicity (bleeding, ulceration, perforation). * **Diarrhea:** Diarrhea is a unique side effect of mefenamic acid compared to other NSAIDs; discontinue immediately if it occurs. *** *Disclaimer: This information is for educational purposes only. Clinical guidelines and local protocols vary significantly. Always verify specific dosing, safety profiles, and updated prescribing information via reliable institutional resources or the product package insert before prescribing or administering medication.*