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# Mefenamic Acid ## Overview Mefenamic acid is a nonsteroidal anti-inflammatory drug (NSAID) that exerts its effect primarily through the inhibition of cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis. ## Primary Indications * Treatment of primary dysmenorrhea. * Short-term management of mild to moderate pain (not to exceed 1 week of therapy). ## Adult Dosing * **Dysmenorrhea:** 500 mg initially, followed by 250 mg every 6 hours as needed. * **Pain:** 500 mg initially, followed by 250 mg every 6 hours as needed. * **Maximum Dose:** Do not exceed 1 week of continuous therapy. ## Pediatric Dosing * **Adolescents (≥14 years):** Dosing is the same as adult dosing. * **Under 14 years:** Safety and efficacy have not been established. Use is generally not recommended in this population. ## Dose Adjustments * **Renal Impairment:** Avoid in patients with severe renal impairment (CrCl <30 mL/min). Use with caution in mild-to-moderate impairment; dose reduction may be required based on clinical response. * **Hepatic Impairment:** Use with caution; monitor for signs of hepatic toxicity. ## Contraindications * Known hypersensitivity (e.g., anaphylaxis, asthma) to mefenamic acid, aspirin, or other NSAIDs. * History of asthma, urticaria, or allergic-type reactions after taking aspirin or other NSAIDs. * Treatment of peri-operative pain in the setting of coronary artery bypass graft (CABG) surgery. * Active peptic ulcer disease or gastrointestinal bleeding. ## Adverse Effects * **Common:** GI distress (nausea, vomiting, diarrhea, abdominal pain), headache. * **Serious:** GI bleeding/ulceration, cardiovascular events (MI, stroke), fluid retention/edema, hypertension, acute renal failure, interstitial nephritis, exfoliative dermatitis, and hepatotoxicity. ## Key Drug Interactions * **Anticoagulants (e.g., Warfarin):** Increased risk of bleeding. * **Antihypertensives (ACE inhibitors, ARBs, diuretics):** Reduced effectiveness; increased risk of acute renal failure. * **Lithium/Methotrexate:** Decreased renal clearance, leading to increased plasma concentrations and potential toxicity. * **Other NSAIDs/Aspirin:** Increased risk of GI toxicity and bleeding. ## Monitoring * Baseline and periodic renal function tests (BUN, creatinine). * Monitor hemoglobin/hematocrit if long-term treatment is anticipated (rare, due to the 7-day limit). * Blood pressure monitoring. * Monitor for signs of GI bleeding (melena, hematemesis). ## Clinical Pearls * **Therapy Limit:** Due to the risk of significant GI side effects and blood dyscrasias, treatment duration is strictly limited to 7 days. * **Administration:** Take with food or milk to minimize gastrointestinal irritation. * **Cardiovascular Risk:** Like all NSAIDs, mefenamic acid carries a boxed warning regarding the increased risk of serious cardiovascular thrombotic events. * **Diarrhea Warning:** Mefenamic acid is uniquely associated with the development of severe, sometimes bloody, diarrhea; discontinue if this occurs. *** *Disclaimer: This information is for educational purposes only. Clinical protocols may vary by institution. Always verify dosages and safety data against current prescribing information or institutional clinical guidelines before administration.*