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# Mefenamic Acid ## Overview Mefenamic acid is a nonsteroidal anti-inflammatory drug (NSAID) of the fenamate class. It possesses analgesic, anti-inflammatory, and antipyretic properties, primarily by inhibiting cyclooxygenase (COX-1 and COX-2) enzymes and reducing prostaglandin synthesis. ## Primary Indications * Treatment of mild-to-moderate pain. * Management of primary dysmenorrhea. * *Note: Treatment duration should not exceed 7 days.* ## Adult Dosing * **Initial Dose:** 500 mg orally as a loading dose. * **Maintenance:** 250 mg orally every 6 hours as needed. * **Maximum Dose:** Do not exceed 1 gram (1000 mg) per day. ## Pediatric Dosing * **Children > 14 years:** Follow adult dosing guidelines (see above). * **Children < 14 years:** Safety and efficacy are not established. Use is generally avoided in this demographic. ## Dose Adjustments * **Renal Impairment:** Avoid in patients with severe renal impairment (CrCl < 30 mL/min). Use with extreme caution in mild-to-moderate impairment; close monitoring of renal function is required. * **Hepatic Impairment:** Avoid in patients with severe hepatic impairment. Reduce dose in mild-to-moderate impairment. * **Elderly:** Use the lowest effective dose for the shortest duration due to increased risk of gastrointestinal (GI) and cardiovascular adverse events. ## Contraindications * Known hypersensitivity to mefenamic acid or aspirin/other NSAIDs. * History of asthma, urticaria, or allergic-type reactions after taking aspirin or other NSAIDs. * Treatment of perioperative pain in the setting of coronary artery bypass graft (CABG) surgery. * Active peptic ulceration or history of recurrent GI ulceration/hemorrhage. * Severe renal, hepatic, or cardiac failure. ## Adverse Effects * **GI:** Diarrhea (common and potentially severe), nausea, abdominal pain, GI ulceration, bleeding/perforation. * **Renal:** Fluid retention, edema, acute renal failure, interstitial nephritis. * **Cardiovascular:** Hypertension, potential increased risk of myocardial infarction and stroke. * **Hematologic:** Anemia, thrombocytopenia, leukopenia. * **General:** Headache, dizziness, skin rash. ## 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 and increased risk of renal impairment. * **Lithium/Methotrexate:** Potential for increased plasma concentrations and toxicity. * **Corticosteroids:** Increased risk of GI ulceration. ## Monitoring * **Renal Function:** Monitor serum creatinine and electrolytes, especially in elderly or comorbid patients. * **GI:** Monitor for signs of occult blood loss or gastric irritation. * **Blood Pressure:** Regular monitoring during chronic use. * **Complete Blood Count:** Periodic monitoring if used for longer durations. ## Clinical Pearls * **Duration:** Therapy is strictly limited to a maximum of 7 days; prolonged use significantly increases toxicity risks. * **GI Symptoms:** Mefenamic acid is notorious for inducing diarrhea; discontinue immediately if severe diarrhea develops. * **Administration:** Take with food or milk to minimize gastric upset. * **Cardiovascular Warning:** Like all NSAIDs, it may increase the risk of serious thrombotic events. Always use the lowest dose for the shortest time required. *** **Educational Disclaimer:** This information is for educational purposes only. Clinical protocols and regulatory labeling may vary by region. Always verify dosing, contraindications, and drug interactions against institutional guidelines and the most current manufacturer-provided package insert before prescribing or administering medication.