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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 inhibition of cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis. Its use is generally limited to short-term therapy (not exceeding 7 days). ## Primary Indications * Primary dysmenorrhea. * Mild to moderate acute pain. ## Adult Dosing * **Initial Dose:** 500 mg orally as a loading dose. * **Maintenance:** 250 mg orally every 6 hours as needed. * **Maximum Duration:** 7 days of treatment. ## Pediatric Dosing * **Children >14 years:** Use adult dosing guidelines. * **Children <14 years:** Safety and efficacy are not established. Use is generally not recommended in this population. ## Dose Adjustments * **Renal Impairment:** Avoid in severe renal impairment (CrCl <30 mL/min). Use with caution and consider dose reduction in mild-to-moderate impairment. * **Hepatic Impairment:** Use with caution; monitor for hepatotoxicity. ## Contraindications * Hypersensitivity to mefenamic acid or other NSAIDs (including aspirin-induced asthma or urticaria). * History of GI bleeding or perforation related to previous NSAID therapy. * Active peptic ulcer disease or inflammatory bowel disease. * Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery. * Severe renal or hepatic impairment. ## Adverse Effects * **Common:** Abdominal pain, nausea, diarrhea, constipation, dyspepsia, dizziness, headache. * **Serious:** GI bleeding, ulceration, or perforation; cardiovascular thrombotic events (myocardial infarction, stroke); hypertension; fluid retention/edema; renal insufficiency; hemolytic anemia (long-term use); hepatotoxicity. ## Key Drug Interactions * **Anticoagulants (e.g., Warfarin):** Increased risk of bleeding. * **Antiplatelet Agents/SSRIs:** Increased risk of GI bleeding. * **ACE Inhibitors/ARBs/Diuretics:** Reduced antihypertensive effect; increased risk of acute kidney injury. * **Lithium/Methotrexate:** Decreased renal clearance, leading to increased plasma concentrations and potential toxicity. ## Monitoring * **Baseline:** Baseline renal function (SCr/CrCl) and hepatic function (LFTs). * **Ongoing:** Monitor for signs of GI bleeding (melena, hematemesis), persistent changes in blood pressure, fluid retention, and worsening renal function. * **Long-term:** CBC to monitor for anemia or blood dyscrasias. ## Clinical Pearls * **GI Protection:** Administer with food or milk to minimize gastrointestinal irritation. * **CV Risk:** All NSAIDs carry a black box warning for increased risk of serious cardiovascular thrombotic events. * **Avoid:** Should be avoided in the third trimester of pregnancy due to the risk of premature closure of the ductus arteriosus. * **Dose Limits:** Exceeding the 7-day treatment duration significantly increases the risk of GI and renal adverse effects. *** *Disclaimer: This information is for educational purposes and does not substitute for professional medical judgment. Always verify current prescribing information, institutional protocols, and patient-specific factors before administering or prescribing any medication.*