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# Mefenamic Acid ## Overview Mefenamic acid is an anthranilic acid derivative nonsteroidal anti-inflammatory drug (NSAID) that inhibits cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis. It possesses analgesic, anti-inflammatory, and antipyretic properties. ## Primary Indications * Treatment of mild to moderate pain. * Primary dysmenorrhea. * Off-label: Management of heavy menstrual bleeding (menorrhagia). ## Adult Dosing * **Pain/Dysmenorrhea:** 500 mg initially, followed by 250 mg every 6 hours as needed. * **Duration:** Therapy should not exceed 7 days. ## Pediatric Dosing * **Children ≥ 14 years:** Follow adult dosing (500 mg initial, then 250 mg every 6 hours). * **Children < 14 years:** Safety and efficacy have not been established. Use is generally not recommended. ## Dose Adjustments * **Renal Impairment:** Use with caution. Generally contraindicated in severe renal failure. Monitor serum creatinine in patients with mild-to-moderate impairment. * **Hepatic Impairment:** Use with caution. Dose reduction may be necessary in mild hepatic impairment; avoid in severe hepatic dysfunction. ## Contraindications * Known hypersensitivity to mefenamic acid, aspirin, or other NSAIDs. * History of asthma, urticaria, or allergic-type reactions after taking aspirin or other NSAIDs. * Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery. * History of gastrointestinal (GI) bleeding or active ulceration. * Severe renal or hepatic impairment. ## Adverse Effects * **Common:** GI upset (nausea, diarrhea, abdominal pain), dizziness, headache. * **Serious:** GI bleeding/ulceration, cardiovascular thrombotic events (myocardial infarction, stroke), hypertension, fluid retention, renal impairment, and blood dyscrasias. * **Note:** Diarrhea is a frequent side effect specific to mefenamic acid and may necessitate discontinuation. ## Key Drug Interactions * **Anticoagulants (e.g., Warfarin):** Increased risk of bleeding. * **Antiplatelet Agents (e.g., Clopidogrel, Aspirin):** Increased risk of GI toxicity and bleeding. * **ACE Inhibitors/ARBs/Diuretics:** May diminish antihypertensive effects and increase risk of drug-induced nephrotoxicity. * **Lithium/Methotrexate:** NSAIDs can decrease renal clearance, increasing systemic toxicity levels. ## Monitoring * Baseline and periodic assessment of renal function (BUN/SCr) and liver enzymes. * Periodic CBC to monitor for hemoglobin/hematocrit stability (potential for occult GI loss). * Monitor blood pressure during initial therapy. * Monitor for signs of GI toxicity (dark, tarry stools, epigastric pain). ## Clinical Pearls * **Short-Term Use:** Due to the risk of severe GI and renal toxicity, therapy is restricted to a maximum of 7 days. * **Administration:** Take with food or milk to minimize GI irritation. * **Cross-Sensitivity:** Due to structural similarities to aspirin, patients with "aspirin-exacerbated respiratory disease" (AERD) are at high risk for bronchospasm. * **Caution:** Avoid in the third trimester of pregnancy (risk of premature closure of the ductus arteriosus). *** **Educational Disclaimer:** This information is for educational purposes only. Always verify dosages and safety guidelines against current institutional protocols, local prescribing information (e.g., FDA labels or the BNF), and the patient's individual clinical profile before prescribing or administering medication.