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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, thereby reducing prostaglandin synthesis. ## Primary Indications * Mild to moderate pain. * Primary dysmenorrhea. * *Note: Use is generally limited to short-term therapy (not exceeding 7 days).* ## Adult Dosing * **Pain/Dysmenorrhea:** 500 mg initially, followed by 250 mg every 6 hours as needed. * **Maximum Dose:** 1,500 mg per day. ## Pediatric Dosing * **Age ≥ 14 years:** Use adult dosing. * **Age < 14 years:** Safety and efficacy are not established; routine use is not recommended. ## Dose Adjustments * **Renal Impairment:** Avoid 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 as the drug is highly protein-bound and extensively metabolized by the liver. ## Contraindications * Hypersensitivity to mefenamic acid, aspirin, or other NSAIDs. * History of asthma, urticaria, or allergic-type reactions after taking aspirin or other NSAIDs. * Active peptic ulceration or inflammatory bowel disease. * Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery. * Severe renal or hepatic failure. ## Adverse Effects * **Common:** Abdominal pain, nausea, vomiting, dizziness, headache, diarrhea (may be severe). * **Serious:** Gastrointestinal (GI) bleeding/ulceration, cardiovascular thrombotic events (myocardial infarction, stroke), renal impairment, hypertension, fluid retention, and hepatotoxicity. ## Key Drug Interactions * **Anticoagulants (e.g., Warfarin):** Increased risk of serious GI bleeding. * **Antiplatelet Agents/SSRIs:** Increased risk of GI bleeding. * **ACE Inhibitors/ARBs/Diuretics:** Reduced antihypertensive effect and increased risk of acute kidney injury. * **Lithium/Methotrexate:** Potential increase in plasma concentrations and toxicity. ## Monitoring * **Renal Function:** Periodic serum creatinine, especially in the elderly or those with chronic kidney disease. * **GI:** Monitor for signs/symptoms of GI ulceration or bleeding (melena, hematemesis). * **Cardiovascular:** Monitor blood pressure; monitor for signs of fluid retention or edema. * **Liver:** Periodic hepatic panel if used for extended periods. ## Clinical Pearls * **Administration:** Take with food or milk to minimize GI irritation. * **Severe Diarrhea:** Mefenamic acid is uniquely associated with the development of severe diarrhea. If diarrhea occurs, the drug should be discontinued promptly. * **Patient Counseling:** Patients should be advised to avoid concurrent use of other NSAIDs or aspirin. * **Limitations:** Due to high GI toxicity and a greater propensity for diarrhea compared to other NSAIDs, it is often considered a second-line agent for pain management. *** *Disclaimer: This information is for educational purposes only. Clinical guidelines and prescribing information change frequently. Always verify specific doses, contraindications, and local protocols against current, authoritative pharmaceutical references or institutional clinical decision support tools before prescribing or administering medication.*