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# Mefenamic Acid ## Overview Mefenamic acid is a nonsteroidal anti-inflammatory drug (NSAID) of the fenamate class. It acts by inhibiting cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis. Its primary use is for short-term management of pain. ## Primary Indications * Primary dysmenorrhea (labeled indication). * Mild to moderate pain (off-label or context-dependent). ## Adult Dosing * **Dysmenorrhea/Pain:** 500 mg initially, followed by 250 mg every 6 hours as needed. * **Duration:** Therapy should not exceed 7 days. ## Pediatric Dosing * **Children ≥14 years:** Use adult dosing schedule. * **Children <14 years:** Safety and efficacy have not been established. Use is generally not recommended. ## Dose Adjustments * **Renal Impairment:** Avoid in severe renal impairment (CrCl <30 mL/min). Use with caution in mild-to-moderate impairment; close monitoring of renal function is required. * **Hepatic Impairment:** Avoid in patients with significant hepatic impairment due to increased risk of toxicity. * **Geriatric:** Use the lowest effective dose for the shortest possible duration. ## Contraindications * Known hypersensitivity to mefenamic acid, aspirin, or other NSAIDs. * History of asthma, urticaria, or allergic-type reactions after taking aspirin or other NSAIDs. * Active peptic ulcer disease or GI bleeding. * Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery. * Severe renal or hepatic failure. ## Adverse Effects * **Common:** Diarrhea (frequent dose-dependent effect), nausea, epigastric pain, headache, dizziness. * **Serious:** Gastrointestinal ulceration/perforation, cardiovascular thrombotic events, nephrotoxicity, hepatotoxicity, fluid retention/edema, severe skin reactions (e.g., Stevens-Johnson syndrome). ## Key Drug Interactions * **Anticoagulants (e.g., Warfarin):** Increased risk of bleeding due to platelet inhibition and gastric mucosal injury. * **ACE Inhibitors/ARBs/Diuretics:** Reduced antihypertensive effect and increased risk of acute kidney injury. * **Methotrexate:** Increased risk of methotrexate toxicity due to reduced renal clearance. * **Other NSAIDs/Corticosteroids:** Increased risk of GI ulceration and bleeding. * **Lithium:** Increased plasma concentrations of lithium. ## Monitoring * Monitor hemoglobin and hematocrit if long-term use is suspected or if signs of occult bleeding occur. * Monitor renal function (SCr, BUN) and electrolytes periodically in high-risk patients. * Monitor blood pressure during initial therapy. * Assess for occult GI signs (e.g., melena, hematemesis). ## Clinical Pearls * **GI Sensitivity:** Mefenamic acid has a higher incidence of diarrhea compared to other NSAIDs; if diarrhea occurs, the dose should be reduced or the drug discontinued. * **Duration Limit:** Due to the risk of hemolytic anemia and severe gastrointestinal adverse effects, therapy is strictly limited to 7 days. * **Administration:** Take with food or milk to minimize gastrointestinal upset. * **Avoid in Pregnancy:** Contraindicated in the third trimester due to the risk of premature closure of the ductus arteriosus. *** *Disclaimer: This information is for educational purposes and does not replace professional clinical judgment. Always consult current institutional protocols, the package insert, and localized prescribing databases (e.g., Lexicomp, UpToDate) before prescribing or administering medication.*