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# Mefenamic Acid ## Overview Mefenamic acid is an anthranilic acid derivative nonsteroidal anti-inflammatory drug (NSAID). It exerts its effects by inhibiting prostaglandin synthesis via the inhibition of cyclooxygenase (COX-1 and COX-2) enzymes. ## Primary Indications * Treatment of primary dysmenorrhea. * Short-term management of mild to moderate pain (usually not exceeding 7 days of therapy). ## Adult Dosing * **Dysmenorrhea/Pain:** 500 mg orally as an initial dose, followed by 250 mg every 6 hours as needed. * **Maximum Dose:** Do not exceed 1,500 mg per day. Treatment duration should be limited to 7 days. ## Pediatric Dosing * **Adolescents (≥14 years):** Dosing is identical to adults (500 mg initial, then 250 mg every 6 hours). * **Children (<14 years):** Safety and efficacy have not been established. Use is generally not recommended in this population. ## Dose Adjustments * **Renal Impairment:** Avoid or exercise extreme caution in patients with significant renal impairment (CrCl <30 mL/min). NSAIDs reduce renal prostaglandin synthesis, which can precipitate acute renal failure. * **Hepatic Impairment:** Use with caution. If used, consider a lower starting dose due to potential for drug accumulation. ## Contraindications * Known hypersensitivity (including asthma, urticaria, or allergic-type reactions) to mefenamic acid, aspirin, or other NSAIDs. * History of GI bleeding or ulceration. * History of asthma induced by aspirin or NSAIDs. * Peri-operative pain in the setting of coronary artery bypass graft (CABG) surgery. * Severe renal impairment or established ischemic heart disease/cerebrovascular disease. ## Adverse Effects * **Gastrointestinal:** Diarrhea (frequent/dose-related), nausea, abdominal pain, dyspepsia, risk of GI ulceration or hemorrhage. * **Renal:** Fluid retention, edema, increased serum creatinine, hematuria. * **Hematologic:** Anemia, leukopenia, thrombocytopenia. * **Systemic:** Hypertension, dizziness, and increased risk of serious cardiovascular thrombotic events (myocardial infarction, stroke). ## Key Drug Interactions * **Anticoagulants (e.g., Warfarin):** Increased risk of bleeding due to antiplatelet effects and GI mucosal injury. * **ACE Inhibitors/ARBs/Diuretics:** Increased risk of renal impairment and potential loss of antihypertensive efficacy. * **Lithium/Methotrexate:** NSAIDs may decrease the renal clearance of these drugs, increasing toxicity risks. * **Corticosteroids/SSRIs:** Synergistic risk of GI ulceration. ## Monitoring * **Baseline/Ongoing:** Periodic assessment of renal function (BUN/SCr), liver function (LFTs), and complete blood count (CBC) during prolonged therapy (though therapy should be short-term). * **Symptoms:** Monitor for signs of GI bleeding (occult blood, melena), cardiovascular symptoms (chest pain, shortness of breath), and signs of fluid retention (edema, weight gain). ## Clinical Pearls * **Diarrhea:** Mefenamic acid has a unique propensity to cause diarrhea; if diarrhea occurs, the drug should be discontinued promptly. * **Duration:** It is strictly indicated for short-term use (≤ 7 days). Chronic use increases the probability of severe adverse outcomes. * **Take with food:** Administer with food or milk to minimize gastrointestinal upset, though this may not entirely prevent ulcers. * **Counseling:** Advise patients to avoid other NSAIDs (including OTC ibuprofen or naproxen) while taking mefenamic acid to reduce the risk of additive toxicity. *** *Disclaimer: This information is for educational purposes only. Clinical practice guidelines and prescribing information change frequently. Always consult the most current manufacturer labeling, institutional protocols, or a clinical pharmacist before finalizing a prescription or treatment plan.*