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# Mefenamic Acid ## Overview Mefenamic acid is an anthranilic acid derivative nonsteroidal anti-inflammatory drug (NSAID) that exhibits analgesic, anti-inflammatory, and antipyretic properties. It acts primarily by inhibiting the cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis. ## Primary Indications * Treatment of primary dysmenorrhea. * Short-term management of mild to moderate pain (typically not exceeding 7 days of therapy). ## Adult Dosing * **Dysmenorrhea/Mild to Moderate Pain:** 500 mg orally as an initial dose, followed by 250 mg orally every 6 hours as needed. * **Maximum Dose:** Do not exceed 1,500 mg per day. Therapy should be limited to 7 days or less to minimize gastrointestinal and renal toxicity. ## Pediatric Dosing * **Children >14 years:** Use adult dosing schedule. * **Children <14 years:** Safety and efficacy have not been established. Use is generally not recommended in this population. ## Dose Adjustments * **Renal Impairment:** Avoid use in patients with severe renal impairment (CrCl <30 mL/min). Use with caution and monitor closely in mild to moderate impairment. * **Hepatic Impairment:** Use with caution; dose reduction may be required. Avoid in severe hepatic impairment. * **Geriatric:** Initiate at the lowest effective dose; monitor for increased risk of GI bleeding and cardiovascular events. ## Contraindications * Known hypersensitivity to mefenamic acid or other NSAIDs (including aspirin-induced asthma or urticaria). * History of GI bleeding, ulceration, or perforation. * Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery. * Severe renal or hepatic failure. * Third trimester of pregnancy (risk of premature closure of the ductus arteriosus). ## Adverse Effects * **Common:** Abdominal pain, nausea, diarrhea, constipation, dyspepsia, dizziness, and headache. * **Serious:** GI bleeding/ulceration, cardiovascular events (MI, stroke), fluid retention/edema, acute renal failure, hypertension, and drug-induced hepatotoxicity. ## Key Drug Interactions * **Anticoagulants (e.g., Warfarin):** Increased risk of major bleeding. * **Other NSAIDs/Aspirin:** Increased risk of GI toxicity and bleeding. * **ACE Inhibitors/ARBs/Diuretics:** Reduced antihypertensive effect and increased risk of acute kidney injury. * **Lithium/Methotrexate:** Increased plasma concentrations and toxicity risk due to reduced renal clearance. ## Monitoring * **Baseline:** Serum creatinine, BUN, and baseline hemoglobin/hematocrit if long-term use is contemplated. * **Ongoing:** Monitor blood pressure, symptoms of GI bleeding (occult blood, anemia), and edema. Periodic evaluation of renal function is recommended during chronic or recurring use. ## Clinical Pearls * **Limited Duration:** Mefenamic acid is strictly intended for short-term use (≤7 days). Chronic use is generally discouraged compared to other NSAIDs due to the higher risk of diarrhea and GI toxicity. * **Administration:** Take with food or milk to reduce gastrointestinal irritation. * **Cardiovascular Risk:** Like all non-aspirin NSAIDs, it carries a boxed warning for increased risk of serious cardiovascular thrombotic events. *** **Educational Disclaimer:** This information is for educational purposes only. Clinical protocols and prescribing information may vary by region and individual patient factors. Always verify current prescribing information, package inserts, and hospital guidelines before administering any medication.