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# Mefenamic Acid ## Overview Mefenamic acid is an anthranilic acid derivative nonsteroidal anti-inflammatory drug (NSAID). It exhibits analgesic, anti-inflammatory, and antipyretic properties by inhibiting cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis. ## Primary Indications * Treatment of mild to moderate pain. * Primary dysmenorrhea. * Short-term management (not exceeding 7 days). ## Adult Dosing * **Initial Dose:** 500 mg orally once. * **Maintenance:** 250 mg orally every 6 hours as needed. * **Maximum Duration:** 7 days. ## Pediatric Dosing * **Children ≥ 14 years:** Use adult dosing regimen. * **Children < 14 years:** Safety and efficacy have not been established; generally not recommended. ## Dose Adjustments * **Renal Impairment:** Use with caution in mild-to-moderate impairment; contraindicated in severe renal failure. * **Hepatic Impairment:** Use with caution; monitor for signs of hepatic toxicity. Close monitoring required in patients with impaired liver function or history of liver disease. ## Contraindications * Hypersensitivity to mefenamic acid or other NSAIDs (including aspirin). * History of asthma, urticaria, or allergic-type reactions after taking aspirin or other NSAIDs. * History of gastrointestinal (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 impairment. ## Adverse Effects * **Common:** Abdominal pain, diarrhea (may be severe), nausea, constipation, dyspepsia, dizziness, and headache. * **Serious:** GI bleeding/ulceration, cardiovascular events (MI, stroke), hypertension, renal toxicity, fluid retention/edema, hepatotoxicity, and serious skin reactions (e.g., Stevens-Johnson syndrome). ## Key Drug Interactions * **Anticoagulants (e.g., Warfarin):** Increases risk of bleeding. * **Aspirin/Other NSAIDs:** Increases risk of GI toxicity and bleeding. * **Antihypertensives (ACE inhibitors, Diuretics):** May diminish the antihypertensive effect; increased risk of renal impairment. * **Lithium/Methotrexate:** May increase serum concentrations and toxicity. * **Corticosteroids:** Concomitant use increases risk of GI ulceration. ## Monitoring * **GI:** Monitor for signs of bleeding (occult blood, anemia). * **Renal:** Monitor serum creatinine and BUN, especially in high-risk patients (elderly, pre-existing renal disease). * **Cardiovascular:** Monitor blood pressure periodically. * **Liver:** Periodically monitor hepatic function tests if used long-term or if symptoms of hepatotoxicity occur. ## Clinical Pearls * **GI Caution:** Due to the risk of severe diarrhea, discontinue immediately if diarrhea occurs. * **Duration:** Always limit use to the shortest duration possible to achieve pain control. * **Food:** Administer with food or milk to decrease GI distress. * **CV Risk:** All NSAIDs carry a black box warning regarding increased risk of serious cardiovascular thrombotic events and GI adverse events. *** **Educational Disclaimer:** This information is for educational purposes only. Always consult current prescribing information (e.g., FDA label or product monograph) and institutional protocols before prescribing or administering medication. Clinical judgment should be exercised based on specific patient history.