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# Mefenamic Acid ## Overview Mefenamic acid is an anthranilic acid derivative nonsteroidal anti-inflammatory drug (NSAID). It possesses analgesic, anti-inflammatory, and antipyretic properties, primarily by inhibiting cyclooxygenase (COX-1 and COX-2) enzymes and reducing prostaglandin synthesis. Its use is limited due to potential gastrointestinal and renal toxicity. ## Primary Indications * Treatment of mild to moderate pain. * Primary dysmenorrhea. ## Adult Dosing * **Initial Dose:** 500 mg orally as a single loading dose. * **Maintenance Dose:** 250 mg orally every 6 hours as needed, not to exceed 1 week of therapy. * **Maximum Dose:** 1,500 mg/day. ## Pediatric Dosing * **Children ≥14 years:** Follow adult dosing guidelines. * **Children <14 years:** Safety and efficacy have not been established; use is generally avoided. ## Dose Adjustments * **Renal Impairment:** Avoid in patients with severe renal impairment (CrCl <30 mL/min). Use with caution in mild-to-moderate impairment. * **Hepatic Impairment:** Avoid in patients with severe hepatic impairment; caution required in mild-to-moderate cases. * **Geriatric:** Use the lowest effective dose for the shortest duration due to increased risk of serious cardiovascular, gastrointestinal, and renal adverse events. ## Contraindications * Known hypersensitivity (e.g., urticaria, bronchospasm, anaphylaxis) to mefenamic acid, aspirin, or other NSAIDs. * History of asthma triggered by NSAIDs. * Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery. * Active peptic ulcer disease or history of recurrent GI ulceration/bleeding. * Severe renal, hepatic, or cardiac failure. * Third trimester of pregnancy. ## Adverse Effects * **Gastrointestinal:** Diarrhea (frequent), nausea, abdominal pain, GI ulceration, bleeding, and perforation. * **Renal:** Fluid retention, edema, acute renal failure, interstitial nephritis. * **Cardiovascular:** Hypertension, increased risk of myocardial infarction and stroke (class effect). * **Hematologic:** Anemia, blood dyscrasias, prolonged bleeding time. * **CNS:** Dizziness, headache, nervousness. ## Key Drug Interactions * **Anticoagulants (e.g., Warfarin):** Increased risk of bleeding due to antiplatelet effects and gastric mucosal injury. * **ACE Inhibitors/ARBs/Diuretics:** Reduced antihypertensive effect; increased risk of nephrotoxicity. * **Lithium:** May increase serum lithium levels, leading to toxicity. * **Methotrexate:** May increase methotrexate levels and toxicity. * **Other NSAIDs/Corticosteroids:** Increased risk of GI toxicity and ulceration. ## Monitoring * **Renal Function:** Periodically monitor serum creatinine and BUN in long-term/chronic use. * **Blood Pressure:** Monitor regularly, as NSAIDs can induce or exacerbate hypertension. * **GI:** Monitor for signs of occult or overt GI bleeding (e.g., melena, hematemesis). * **Hematologic:** Monitor for signs of anemia if prolonged use is necessary. ## Clinical Pearls * **Short Duration:** Mefenamic acid is FDA-labeled for short-term use only (not to exceed 7 days). It is generally not indicated for chronic arthritis conditions. * **GI Sensitivity:** Diarrhea is a common dose-limiting side effect; discontinue if diarrhea develops. * **CV Risk:** All NSAIDs (except aspirin) carry an increased risk of serious cardiovascular thrombotic events. Use at the lowest effective dose for the shortest duration necessary to control symptoms. * **Administration:** Take with food or milk to minimize gastrointestinal upset. *** **Educational Disclaimer:** This information is for educational purposes only and does not constitute medical advice. Mefenamic acid usage and local protocols vary by institution and region. Always consult the latest package insert, official clinical guidelines, or a board-certified pharmacist/physician before prescribing or administering medication.