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# Mefenamic Acid
## Overview
Mefenamic acid is an anthranilic acid derivative nonsteroidal anti-inflammatory drug (NSAID) that exhibits analgesic, anti-inflammatory, and antipyretic properties. Like other NSAIDs, it inhibits cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis.
## Primary Indications
* Treatment of mild to moderate pain (short-term use, typically ≤7 days).
* Treatment of primary dysmenorrhea.
## Adult Dosing
* **Pain/Dysmenorrhea:** 500 mg initially, followed by 250 mg every 6 hours as needed.
* **Maximum Dose:** Do not exceed 1,500 mg per day or use for longer than 1 week.
## Pediatric Dosing
* **Adolescents (≥14 years):** Same as adult dosing.
* **Children (<14 years):** Safety and efficacy have not been established. Use is generally not recommended.
## Dose Adjustments
* **Renal Impairment:** Avoid in patients with severe renal impairment (CrCl <30 mL/min). Monitor closely in moderate impairment.
* **Hepatic Impairment:** Use with caution; monitor for signs of hepatic toxicity. Dose reduction may be required.
* **Elderly:** Use the lowest effective dose for the shortest duration due to increased risk of gastrointestinal (GI) and cardiovascular adverse effects.
## Contraindications
* Known hypersensitivity to mefenamic acid or other NSAIDs (including aspirin-induced asthma/urticaria).
* History of GI bleeding or perforation related to previous NSAID therapy.
* Active peptic ulcer disease or inflammatory bowel disease.
* Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery.
* Severe renal or hepatic failure.
## Adverse Effects
* **Common:** Nausea, diarrhea, abdominal pain, dyspepsia, headache, dizziness.
* **Serious:** GI ulceration/bleeding, myocardial infarction, stroke, renal insufficiency, hepatotoxicity, fluid retention/edema, severe skin reactions (e.g., SJS/TEN - rare).
## Key Drug Interactions
* **Anticoagulants (e.g., Warfarin):** Increased risk of bleeding.
* **ACE Inhibitors/ARBs/Diuretics:** Reduced antihypertensive effect and increased risk of acute renal failure.
* **Lithium/Methotrexate:** Decreased clearance, potentially leading to toxicity.
* **Other NSAIDs/Corticosteroids:** Increased risk of GI ulceration and bleeding.
## Monitoring
* Baseline and periodic assessment of renal function (BUN/SCr).
* Monitor for signs of GI bleeding (black/tarry stools, anemia) and fluid retention.
* Monitor blood pressure during long-term therapy.
* Discontinue if abnormal liver function tests persist or worsen.
## Clinical Pearls
* **Administration:** Take with food or milk to minimize gastrointestinal upset.
* **Short-term Use:** Strictly limit duration to avoid the cumulative risk of GI toxicity and nephrotoxicity.
* **Diarrhea:** Mefenamic acid is known to cause dose-related diarrhea, which resolves upon discontinuation.
* **Cross-reactivity:** Use with extreme caution in patients with "aspirin-triad" (asthma, nasal polyps, aspirin sensitivity).
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**Educational Disclaimer:** This information is for educational purposes only. Clinical practice protocols may vary. Always verify current prescribing information, contraindications, and drug-drug interactions through official sources (e.g., package inserts, Lexicomp, or UpToDate) before prescribing or administering medication.
