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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, which reduces prostaglandin synthesis. ## Primary Indications * Treatment of mild to moderate pain. * Primary dysmenorrhea. * *Note: Duration of therapy should not exceed 7 days.* ## Adult Dosing * **Initial Dose:** 500 mg orally. * **Maintenance Dose:** 250 mg orally every 6 hours as needed. * **Maximum Daily Dose:** Do not exceed 1000 mg/day. ## Pediatric Dosing * **Children ≥ 14 years:** Use adult dosing guidelines (see above). * **Children < 14 years:** Safety and efficacy have not been established. Use is generally not recommended unless directed by a specialist. ## Dose Adjustments * **Renal Impairment:** Avoid in patients with severe renal impairment (CrCl < 30 mL/min). Use with caution and consider dose reduction for mild-to-moderate impairment. * **Hepatic Impairment:** Use with caution; monitor for signs of hepatic toxicity. * **Elderly:** Use the lowest effective dose for the shortest duration due to increased risk of gastrointestinal, renal, and cardiovascular adverse effects. ## Contraindications * Known hypersensitivity to mefenamic acid or aspirin/NSAIDs. * History of asthma, urticaria, or allergic-type reactions after taking aspirin or other NSAIDs. * Active peptic ulcer disease or gastrointestinal bleeding. * Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery. * Severe renal or hepatic failure. ## Adverse Effects * **Common:** GI upset (diarrhea is common with mefenamic acid), nausea, abdominal pain, dizziness, and headache. * **Serious:** Gastrointestinal bleeding/ulceration, cardiovascular thrombotic events (myocardial infarction, stroke), hypertension, fluid retention, renal impairment, and severe cutaneous reactions (e.g., Stevens-Johnson syndrome). ## Key Drug Interactions * **Anticoagulants (e.g., Warfarin):** Increased risk of bleeding. * **Antiplatelet agents/SSRIs:** Increased risk of GI bleeding. * **ACE inhibitors/ARBs/Diuretics:** Decreased antihypertensive effect and increased risk of renal impairment (nephrotoxicity). * **Lithium/Methotrexate:** Potential for increased serum concentrations and toxicity due to reduced renal excretion. ## Monitoring * Monitor hemoglobin/hematocrit if long-term therapy (up to the 7-day limit) occurs to detect occult blood loss. * Monitor renal function (BUN/SCr) and blood pressure regularly. * Assess for occult GI bleeding or signs of cardiovascular events. ## Clinical Pearls * **GI Profile:** Mefenamic acid is uniquely associated with a higher incidence of diarrhea compared to other NSAIDs; discontinue immediately if severe, persistent diarrhea occurs. * **Food Intake:** Take with food or milk to minimize gastrointestinal upset. * **CV Risk:** Use with caution in patients with cardiovascular disease or risk factors for cardiovascular disease. *** *Educational Disclaimer: This information is for educational purposes and does not substitute for professional medical judgment. Always verify current prescribing information, institutional protocols, and local drug monographs before prescribing or administering medication.*