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# Mefenamic Acid ## Overview Mefenamic acid is a nonsteroidal anti-inflammatory drug (NSAID) that acts as a cyclooxygenase (COX-1 and COX-2) inhibitor. It possesses analgesic, anti-inflammatory, and antipyretic properties. Because of its limited indication duration (typically ≤7 days) and potential for gastrointestinal toxicity, it is rarely a first-line agent. ## Primary Indications * Treatment of mild to moderate pain. * Treatment of primary dysmenorrhea. ## Adult Dosing * **Acute Pain/Dysmenorrhea:** 500 mg orally initially, followed by 250 mg every 6 hours as needed. * **Maximum Duration:** Do not exceed 7 days of continuous therapy. * **Maximum Dose:** 1,500 mg per day. ## Pediatric Dosing * **Age ≥ 14 years:** Same as adult dosing. * **Age < 14 years:** Safety and efficacy have not been established. Usage is generally avoided. ## Dose Adjustments * **Renal Impairment:** Avoid in patients with severe renal impairment (CrCl < 30 mL/min). Use with caution in mild-to-moderate impairment; monitor closely. * **Hepatic Impairment:** Use with caution. Consider lower doses or alternative agents, as mefenamic acid is highly protein-bound and extensively metabolized by the liver. ## Contraindications * Known hypersensitivity to mefenamic acid or aspirin/NSAIDs. * History of asthma, urticaria, or allergic-type reactions after taking aspirin or other NSAIDs. * History of GI bleeding or perforation related to previous NSAID therapy. * Active peptic ulcer disease or inflammatory bowel disease (IBD). * Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery. * Severe renal or hepatic failure. ## Adverse Effects * **Gastrointestinal:** Dyspepsia, nausea, abdominal pain, diarrhea (common, often dose-limiting), potential for GI ulceration/bleeding. * **Cardiovascular:** Hypertension, fluid retention/edema; increased risk of serious CV thrombotic events (MI, stroke). * **Renal:** Acute kidney injury, interstitial nephritis, hyperkalemia. * **Hematologic:** Potential for blood dyscrasias and inhibition of platelet aggregation. ## Key Drug Interactions * **Anticoagulants (e.g., Warfarin):** Increases risk of bleeding. * **Antiplatelet agents/SSRIs:** Increases risk of GI bleeding. * **ACE Inhibitors/ARBs/Diuretics:** May diminish the antihypertensive effect and increase the risk of renal failure. * **Lithium:** May increase lithium serum concentrations, leading to toxicity. * **Methotrexate:** Increases risk of methotrexate toxicity due to reduced renal clearance. ## Monitoring * Baseline and periodic assessment of renal function (SCr, BUN) and LFTs. * Blood pressure monitoring. * Periodic CBC to monitor for unexplained anemia (signs of occult GI bleed). * Monitor for signs/symptoms of GI ulceration (melena, hematemesis). ## Clinical Pearls * **GI Sensitivity:** Mefenamic acid is notably more likely to cause diarrhea than other NSAIDs. * **Short-term only:** Due to the risk of significant GI and hematologic adverse effects, it is strictly intended for short-term management. * **CV Risk:** All NSAIDs carry a boxed warning for increased risk of serious cardiovascular thrombotic events. * **Administration:** Take with food or milk to minimize potential gastric irritation. *** *Disclaimer: This information is for educational purposes and does not replace professional clinical judgment. Always consult the most current product monograph, institutional guidelines, and official labeling (e.g., FDA/EMA) before prescribing or administering medication.*