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# Mefenamic Acid ## Overview Mefenamic acid is an anthranilic acid derivative nonsteroidal anti-inflammatory drug (NSAID). It exerts its effects by inhibiting cyclooxygenase (COX-1 and COX-2) enzymes, leading to decreased prostaglandin synthesis. It has a relatively short duration of action and a strict limitation on treatment duration. ## Primary Indications * Treatment of primary dysmenorrhea. * Short-term management of mild to moderate pain (typically not exceeding 1 week). ## Adult Dosing * **Dysmenorrhea/Pain:** 500 mg orally as an initial dose, followed by 250 mg every 6 hours as needed. * **Maximum Duration:** Do not exceed 7 days of continuous therapy. ## Pediatric Dosing * **Children ≥14 years:** Use adult dosing guidelines. * **Children <14 years:** Safety and efficacy have not been established. Use is generally avoided in this demographic. ## Dose Adjustments * **Renal Impairment:** Avoid use in patients with severe renal impairment (CrCl <30 mL/min). Use with caution in mild-to-moderate impairment; monitor renal function closely. * **Hepatic Impairment:** Use with caution. Consider lower doses or avoiding use in patients with significant hepatic dysfunction. ## Contraindications * Known hypersensitivity to mefenamic acid or other NSAIDs (including aspirin-induced asthma/urticaria). * History of asthma precipitated by NSAIDs. * Treatment of perioperative pain in the setting of coronary artery bypass graft (CABG) surgery. * Active peptic ulcer disease or history of recurrent gastrointestinal (GI) ulceration/bleeding. * Active inflammatory bowel disease. * Severe renal or hepatic failure. * Third trimester of pregnancy (risk of premature closure of the ductus arteriosus). ## Adverse Effects * **GI:** Diarrhea (common), abdominal pain, nausea, peptic ulceration, GI hemorrhage. * **Renal:** Fluid retention, edema, acute renal failure, interstitial nephritis. * **Cardiovascular:** Hypertension, increased risk of serious thrombotic events (myocardial infarction, stroke). * **Hematologic:** Anemia, blood dyscrasias. * **CNS:** Dizziness, headache, nervousness. ## Key Drug Interactions * **Anticoagulants/Antiplatelets (e.g., Warfarin, Clopidogrel):** Increased risk of bleeding. * **Antihypertensives (ACE inhibitors, ARBs, Diuretics):** Diminished antihypertensive effect; increased risk of nephrotoxicity. * **Lithium:** May increase serum lithium levels, potentially leading to toxicity. * **Methotrexate:** Increased risk of methotrexate toxicity due to reduced renal clearance. * **Corticosteroids/SSRIs:** Increased risk of gastrointestinal ulceration and bleeding. ## Monitoring * **Baseline/Periodic:** Renal function (BUN/SCr), liver function tests, hemoglobin/hematocrit (if long-term use is unavoidable), and blood pressure. * **Symptomatic:** Watch for signs of GI bleeding (melena, hematemesis), fluid retention, or allergic skin reactions. ## Clinical Pearls * **GI Profile:** Mefenamic acid is uniquely noted for causing diarrhea more frequently than other NSAIDs; if this occurs, the drug should be discontinued immediately. * **Duration:** Due to the risk of dose-dependent toxicity, strictly adhere to the 7-day limit. * **Administration:** Take with food or milk to minimize GI irritation. * **CV Warning:** All NSAIDs carry a boxed warning for increased risk of serious cardiovascular thrombotic events. Use the lowest effective dose for the shortest duration necessary. *** *Disclaimer: This information is for educational purposes only. Clinical practice guidelines and drug information can change Frequently. Always consult the latest version of the manufacturer’s package insert, local institutional protocols, or a reliable clinical drug database (e.g., Lexicomp or Micromedex) before prescribing or administering medication.*