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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. ## Primary Indications * Short-term management of mild to moderate pain (usually ≤7 days). * Treatment of primary dysmenorrhea. ## Adult Dosing * **Standard Dose:** 500 mg orally as an initial dose, followed by 250 mg every 6 hours as needed. * **Maximum Dose:** Do not exceed 1000 mg per day or use for longer than 7 consecutive days. ## Pediatric Dosing * **Children ≥14 years:** Use adult dosing guidelines. * **Children <14 years:** Efficacy and safety have not been established. Use is generally not recommended. ## Dose Adjustments * **Renal Impairment:** Avoid use in patients with severe renal impairment (CrCl <30 mL/min). Use with caution in mild-to-moderate impairment; close monitoring of renal function is required. * **Hepatic Impairment:** Use with caution. Consider lower doses as the drug is extensively metabolized by the liver. ## Contraindications * Known 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 failure. * Third trimester of pregnancy (risk of premature closure of the ductus arteriosus). ## Adverse Effects * **Gastrointestinal:** Nausea, vomiting, diarrhea (may be severe), abdominal pain, dyspepsia, risk of GI ulceration/bleeding. * **Cardiovascular:** Hypertension, fluid retention, increased risk of thrombotic events (MI, stroke). * **Renal:** Acute kidney injury, interstitial nephritis, hyperkalemia. * **Hematologic:** Potential for transient leukopenia, thrombocytopenia, or hemolytic anemia with long-term use. ## Key Drug Interactions * **Anticoagulants (e.g., Warfarin):** Increased risk of bleeding. * **Antiplatelet Agents/SSRIs:** Increased risk of GI bleeding. * **Antihypertensives (ACE inhibitors, ARBs, Beta-blockers, Diuretics):** NSAIDs may reduce the antihypertensive efficacy and increase risk of renal impairment. * **Lithium/Methotrexate:** NSAIDs may decrease the renal clearance of these drugs, leading to toxicity. ## Monitoring * **Renal Function:** Monitor serum creatinine and BUN in patients with pre-existing renal disease or those on long-term therapy. * **Blood Pressure:** Monitor for new-onset or worsening hypertension. * **GI Health:** Assess for symptoms of GI distress or occult bleeding. * **Complete Blood Count (CBC):** Periodically if long-term treatment is necessary (rare, but recommended due to the potential for hematologic shift). ## Clinical Pearls * Take with food or milk to minimize gastrointestinal upset. * Mefenamic acid is associated with a higher incidence of diarrhea compared to other NSAIDs. * It is strictly intended for short-term use; chronic use increases the risk of serious CV and GI adverse events significantly. * Avoid concomitant use with other NSAIDs (including aspirin) to minimize additive toxicity. *** *Disclaimer: This information is for educational purposes and does not replace professional clinical judgment. Always verify current prescribing information, institutional protocols, and patient-specific factors before administering any medication.*