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# Mefenamic acid ## Overview Mefenamic acid is a nonsteroidal anti-inflammatory drug (NSAID) used for the short-term management of mild to moderate pain. Its mechanism of action involves the inhibition of cyclooxygenase (COX) enzymes, reducing prostaglandin synthesis. ## Primary Indications * Short-term treatment of mild to moderate pain, particularly dysmenorrhea. * Management of pain associated with osteoarthritis and rheumatoid arthritis (less common due to GI risks). ## Adult Dosing * **Pain:** 500 mg every 6 hours as needed. Treatment should not exceed 7 days. * **Dysmenorrhea:** 500 mg every 4-6 hours as needed, starting at the onset of pain or bleeding. * **Maximum Daily Dose:** 1500 mg (or 2000 mg in specific situations, though generally not recommended for routine use). ## Pediatric Dosing Mefenamic acid is generally not recommended for use in children under 14 years of age due to insufficient data and potential risks. For specific indications like pediatric rheumatic diseases, dosing may be established by specialist guidelines, typically ranging from 5-7 mg/kg/dose every 6-8 hours. **Consult specific pediatric guidelines or a pediatric specialist.** ## Dose Adjustments * **Renal Impairment:** Use with caution. Dose reduction may be necessary; avoid in severe renal impairment. * **Hepatic Impairment:** Use with caution. Dose reduction may be necessary; avoid in severe hepatic impairment. * **Elderly:** Increased risk of GI bleeding, renal, and cardiovascular events. Use lowest effective dose and shortest duration. ## Contraindications * Known hypersensitivity to mefenamic acid, aspirin, or other NSAIDs. * History of NSAID-induced bronchospasm, urticaria, or allergic-type reactions. * Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery. * Active gastrointestinal bleeding or history of recurrent gastrointestinal perforation or ulceration. * Severe renal impairment. * Severe hepatic impairment. * Severe heart failure. * Third trimester of pregnancy. ## Adverse Effects * **Gastrointestinal:** Dyspepsia, nausea, vomiting, diarrhea, constipation, abdominal pain, peptic ulceration, gastrointestinal bleeding, perforation. * **Central Nervous System:** Dizziness, headache, drowsiness. * **Renal:** Acute kidney injury, interstitial nephritis, papillary necrosis. * **Cardiovascular:** Increased risk of myocardial infarction, stroke, and edema. * **Hematologic:** Anemia, leukopenia, thrombocytopenia. * **Dermatologic:** Rash, pruritus. * **Hepatic:** Elevated liver enzymes, jaundice. * **Other:** Bronchospasm (especially in aspirin-sensitive asthmatics), tinnitus. ## Key Drug Interactions * **Anticoagulants (e.g., warfarin):** Increased risk of bleeding. * **Corticosteroids:** Increased risk of GI ulceration and bleeding. * **Selective Serotonin Reuptake Inhibitors (SSRIs):** Increased risk of GI bleeding. * **Other NSAIDs (including aspirin):** Increased risk of adverse effects, particularly GI bleeding. * **Diuretics, ACE inhibitors, Angiotensin II Receptor Blockers (ARBs):** May reduce antihypertensive effect and increase risk of renal impairment. * **Lithium, Methotrexate:** Increased serum concentrations and toxicity. * **Cytochrome P450 Enzyme Inhibitors/Inducers:** Potential for altered mefenamic acid metabolism. ## Monitoring * **Renal function:** Particularly in elderly patients or those with pre-existing renal disease. * **Liver function:** Especially with long-term use or in patients with hepatic impairment. * **Signs and symptoms of GI bleeding:** Occult blood in stool, melena, hematemesis. * **Blood pressure:** NSAIDs can cause hypertension. * **Signs of cardiovascular events:** Chest pain, shortness of breath. ## Clinical Pearls * Mefenamic acid is intended for short-term use only. * Administer with food or milk to minimize gastrointestinal upset. * Avoid concurrent use with other NSAIDs. * Discontinue if signs of renal toxicity, hepatic toxicity, or severe adverse reactions occur. * Should not be used in patients with a history of aspirin-induced asthma. *** **Disclaimer:** This information is intended for clinical use and does not replace the need to consult the official prescribing information (package insert) for the most current and complete details. Always verify current drug information before prescribing or dispensing.