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# Mefenamic Acid ## Overview Mefenamic acid is an anthranilic acid derivative nonsteroidal anti-inflammatory drug (NSAID). It exerts anti-inflammatory, analgesic, and antipyretic effects primarily through the inhibition of cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis. ## Primary Indications * Treatment of primary dysmenorrhea. * Short-term management of mild-to-moderate pain (use duration should not exceed one week). ## Adult Dosing * **Dysmenorrhea/Pain:** 500 mg initially, followed by 250 mg every 6 hours as needed. * **Maximum Dose:** 1,500 mg per 24 hours. * **Duration:** Limit therapy to 7 days or less. ## 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 and consider dose reduction for mild-to-moderate impairment. * **Hepatic Impairment:** Avoid in severe hepatic impairment. Monitor closely for signs of hepatotoxicity. ## Contraindications * Known hypersensitivity to mefenamic acid, aspirin, or other NSAIDs (risk of anaphylaxis/bronchospasm). * History of asthma, urticaria, or allergic-type reactions after taking aspirin or other NSAIDs. * CABG surgery (perioperative pain management). * Active peptic ulcer disease or history of GI bleeding. * Severe renal or hepatic failure. ## Adverse Effects * **Gastrointestinal:** Dyspepsia, nausea, vomiting, abdominal pain, diarrhea (noted to be more common with mefenamic acid than other NSAIDs), and potential GI ulceration or hemorrhage. * **Cardiovascular:** Hypertension, fluid retention, or increased risk of thrombotic events (myocardial infarction, stroke). * **Renal:** Acute kidney injury, interstitial nephritis, or papillary necrosis. * **Hematologic:** Anemia, thrombocytopenia, or prolonged bleeding time. ## Key Drug Interactions * **Anticoagulants (e.g., Warfarin):** Increased risk of bleeding. * **Antiplatelets (e.g., Aspirin, Clopidogrel):** Increased risk of GI toxicity and bleeding. * **ACE Inhibitors/ARBs/Diuretics:** Reduced antihypertensive efficacy and increased risk of acute renal failure. * **Lithium/Methotrexate:** NSAIDs may decrease the renal clearance of these drugs, increasing toxic levels. ## Monitoring * **Periodic:** Renal function (BUN/SCr), CBC (if long-term usage), and blood pressure. * **Symptom-based:** Monitor for evidence of GI toxicity (melena, hematemesis), signs of fluid retention (edema), or allergic responses. ## Clinical Pearls * **Diarrhea:** Mefenamic acid is uniquely associated with the development of diarrhea; if it occurs, the drug should be discontinued promptly. * **Food:** Administration with food or milk may decrease GI irritation, though it may delay peak absorption. * **Pregnancy:** Avoid throughout the pregnancy, especially after 30 weeks gestation, due to the risk of premature closure of the fetal ductus arteriosus and potential oligohydramnios. * **Systemic Efficacy:** No evidence suggests mefenamic acid is more effective than other NSAIDs for general pain; its use is often limited by its specific GI side effect profile. *** **Educational Disclaimer:** This information is for educational purposes only. Drug information, protocols, and safety guidelines are subject to change. Always verify current prescribing information, institutional protocols, and specific patient contraindications via drug databases (e.g., Lexicomp, UpToDate) or the official product insert before prescribing or administering medication.