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# Mefenamic Acid ## Overview Mefenamic acid is a nonsteroidal anti-inflammatory drug (NSAID) belonging to the anthranilic acid derivative class. It possesses analgesic, anti-inflammatory, and antipyretic properties. Its mechanism of action involves the inhibition of cyclooxygenase (COX) enzymes, thereby reducing prostaglandin synthesis. ## Primary Indications * Short-term management of mild to moderate pain, including menstrual pain (dysmenorrhea). * Symptomatic relief of rheumatoid arthritis and osteoarthritis. ## Adult Dosing * **Pain:** 500 mg every 6 hours as needed. Do not exceed 1500 mg daily for acute pain conditions. * **Dysmenorrhea:** 500 mg every 6 hours, starting at the onset of pain and bleeding, and continuing for up to 3 days. * **Rheumatoid Arthritis/Osteoarthritis:** 750 mg every 6 hours initially, may be reduced to 500 mg every 6 hours. Maximum dose: 1500 mg daily. ## Pediatric Dosing Mefenamic acid is generally not recommended for children under 14 years of age due to limited safety and efficacy data. Some sources suggest use in children 6 months and older, but specific dosing is not well-established and typically relies on weight-based calculations extrapolated from adult data, which requires expert consultation and careful monitoring. ## Dose Adjustments * **Renal Impairment:** Use with caution. Reduced doses may be necessary, especially in severe impairment. Data is limited. * **Hepatic Impairment:** Use with caution. Reduced doses may be necessary, especially in severe impairment. Data is limited. * **Geriatric Patients:** Use with caution. Increased risk of adverse effects, particularly gastrointestinal bleeding and renal toxicity. Lower doses may be considered. ## Contraindications * Hypersensitivity to mefenamic acid or other NSAIDs. * History of bronchospasm, asthma, urticaria, or allergic-type reactions after aspirin or other NSAIDs. * Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery. * Active peptic ulceration or history of recurrent gastrointestinal bleeding. * Severe renal or hepatic impairment. * Third trimester of pregnancy. ## Adverse Effects Common adverse effects include: diarrhea, nausea, vomiting, abdominal pain, constipation, dyspepsia, headache, dizziness, rash, and somnolence. Serious adverse effects include: * **Gastrointestinal:** GI bleeding, ulceration, perforation. * **Cardiovascular:** Myocardial infarction, stroke, fluid retention, hypertension. * **Renal:** Renal papillary necrosis, interstitial nephritis, renal failure. * **Hepatic:** Hepatic dysfunction, jaundice. * **Dermatologic:** Stevens-Johnson syndrome, toxic epidermal necrolysis. * **Hematologic:** Anemia, leukopenia. * **Hypersensitivity:** Anaphylaxis, angioedema. ## Key Drug Interactions * **Anticoagulants (e.g., warfarin):** Increased risk of bleeding. * **Corticosteroids:** Increased risk of GI ulceration and bleeding. * **Aspirin:** May decrease the antiplatelet effect of aspirin and increase risk of GI bleeding. * **Diuretics:** Reduced diuretic efficacy; increased risk of nephrotoxicity. * **ACE Inhibitors/ARBs:** Increased risk of renal impairment and hyperkalemia. * **Lithium:** Increased serum lithium levels, potential for toxicity. * **Methotrexate:** Increased methotrexate levels and toxicity. ## Monitoring * **For chronic use:** Monitor for signs and symptoms of GI bleeding (melena, hematemesis), renal function (BUN, creatinine), liver function (AST, ALT), and blood pressure. * **For acute use:** Monitor for efficacy and onset of adverse effects. ## Clinical Pearls * Due to a higher incidence of diarrhea, mefenamic acid is often considered a second-line agent for pain management compared to other NSAIDs. * Should be taken with food or milk to minimize GI upset. * Duration of use should be as short as possible. * Effectiveness and safety in pediatric patients are not well-established. *** *Disclaimer: This information is intended for clinical use by healthcare professionals and is not a substitute for professional medical advice. Always consult the most current prescribing information and relevant literature before making clinical decisions. Dosing and recommendations may vary based on patient-specific factors and local protocols.*