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# Mefenamic Acid ## Overview Mefenamic acid is an anthranilic acid derivative nonsteroidal anti-inflammatory drug (NSAID). It exerts anti-inflammatory, analgesic, and antipyretic effects primarily through the inhibition of cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis. ## Primary Indications * Treatment of mild to moderate pain. * Management of primary dysmenorrhea. * *Note: FDA-approved duration is limited to no more than 7 days.* ## Adult Dosing * **Pain/Dysmenorrhea:** 500 mg orally initially, followed by 250 mg every 6 hours as needed. * **Maximum Dose:** 1,500 mg per day. ## Pediatric Dosing * **Adolescents (≥14 years):** Same as adult dosing. * **Children (<14 years):** Safety and efficacy are not established. Use is generally avoided due to lack of longitudinal safety data in this population. ## 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 extreme caution. Discontinue if abnormal liver function tests persist or worsen. ## Contraindications * Known hypersensitivity (including asthma, urticaria, or allergic-type reactions) to mefenamic acid, aspirin, or other NSAIDs. * History of asthma precipitated by aspirin/NSAIDs. * Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery. * Active peptic ulcer disease or gastrointestinal bleeding. * Severe renal or hepatic impairment. ## Adverse Effects * **Common:** Abdominal pain, constipation, diarrhea, nausea, dyspepsia, dizziness, headache. * **Serious:** Gastrointestinal bleeding/ulceration, cardiovascular events (MI, stroke), fluid retention/edema, acute renal failure, hepatotoxicity, skin reactions (Stevens-Johnson Syndrome). ## Key Drug Interactions * **Anticoagulants (e.g., Warfarin):** Increased risk of bleeding. * **Antiplatelets/SSRIs:** Increased risk of GI toxicity/bleeding. * **ACE Inhibitors/ARBs/Diuretics:** Diminished antihypertensive effect; increased risk of renal impairment. * **Lithium/Methotrexate:** NSAIDs may increase plasma concentrations and toxicity risk. * **Avoid:** Concomitant use with other NSAIDs (including aspirin) to minimize additive toxicity. ## Monitoring * **Baseline/Intermittent:** Renal function (creatinine, BUN), liver function tests, electrolytes, and CBC (if long-term/chronic use occurs). * **Ongoing:** Monitor for signs of GI bleeding (melena, hematemesis), blood pressure control, and peripheral edema. ## Clinical Pearls * **Short-Term Use:** Mefenamic acid is indicated for short-term use only (maximum 7 days). Chronic use significantly increases the risk of serious GI and cardiovascular adverse events. * **Administration:** Take with food or milk to minimize potential gastrointestinal irritation. * **CV Risk:** Like all non-aspirin NSAIDs, mefenamic acid carries a Black Box Warning for an increased risk of serious cardiovascular thrombotic events and serious GI adverse events. * **Caution:** Should be used with caution in patients with fluid retention or hypertension. *** **Educational Disclaimer:** This information is for educational purposes only. Drug information, protocols, and clinical standards change frequently. Always verify current prescribing information, institutional guidelines, and contraindications via official sources (e.g., FDA label, UpToDate, or Lexicomp) before prescribing or administering medication.