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# Mefenamic acid
## Overview
Mefenamic acid is a nonsteroidal anti-inflammatory drug (NSAID) of the fenamate class. It acts by inhibiting cyclooxygenase (COX-1 and COX-2) enzymes, leading to decreased prostaglandin synthesis. It possesses analgesic, anti-inflammatory, and antipyretic properties.
## Primary Indications
* Treatment of primary dysmenorrhea.
* Short-term management of mild to moderate pain (usually ≤7 days).
## Adult Dosing
* **Dysmenorrhea/Pain:** 500 mg orally initially, followed by 250 mg every 6 hours as needed.
* **Maximum Daily Dose:** Do not exceed 1,500 mg per day. Therapy should not exceed 7 days duration.
## Pediatric Dosing
* **Adolescents (≥14 years):** Same as adult dosing.
* **Children (<14 years):** Safety and efficacy have not been established. Use is generally avoided.
## Dose Adjustments
* **Renal Impairment:** Avoid in patients with severe renal impairment (CrCl <30 mL/min). Use with caution in mild-to-moderate impairment; monitor renal function closely.
* **Hepatic Impairment:** Use with caution. Consider lower doses as the drug is extensively metabolized in the liver. May need to be avoided in active liver disease.
* **Geriatric:** Use the lowest effective dose for the shortest duration due to increased risk of GI bleeding and cardiovascular events.
## Contraindications
* Known hypersensitivity to mefenamic acid or other NSAIDs (including aspirin-induced asthma/urticaria).
* History of CABG (coronary artery bypass graft) surgery.
* Active peptic ulcer disease or gastrointestinal bleeding.
* Severe renal or hepatic failure.
* Third trimester of pregnancy (risk of premature closure of the ductus arteriosus).
## Adverse Effects
* **Common:** Abdominal pain, nausea, diarrhea (often dose-related), dizziness, headache.
* **Serious:** Gastrointestinal ulceration/perforation, myocardial infarction, stroke, new-onset hypertension, acute renal failure, interstitial nephritis, fluid retention/edema, and blood dyscrasias (e.g., hemolytic anemia).
## Key Drug Interactions
* **Anticoagulants (e.g., Warfarin):** Increases risk of serious GI bleeding.
* **ACE Inhibitors/ARBs/Diuretics:** Decreased antihypertensive effect; increased risk of acute kidney injury (the "triple whammy").
* **Lithium:** May increase serum lithium concentrations to toxic levels.
* **Methotrexate:** Increases risk of methotrexate toxicity due to reduced renal clearance.
* **Other NSAIDs/Corticosteroids:** Significantly increases risk of GI ulceration and bleeding.
## Monitoring
* Baseline and periodic serum creatinine/BUN in chronic/at-risk patients.
* Monitor hemoglobin/hematocrit if long-term use is suspected (though use is intended for <7 days).
* Blood pressure monitoring, specifically in patients with hypertension.
* Monitor for signs of GI bleeding (melena, hematemesis).
## Clinical Pearls
* **GI Protection:** Administer with food or milk to minimize gastric irritation.
* **Duration:** Strict adherence to a maximum 7-day course is essential to mitigate the risk of severe GI and renal toxicity.
* **Diarrhea:** Mefenamic acid is uniquely associated with persistent, sometimes severe, diarrhea; discontinue if this occurs.
* **Efficacy:** If pain is not adequately controlled with the initial dose, do not exceed the recommended total daily dose of 1,500 mg.
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*Disclaimer: This information is for educational purposes only. Clinical practice protocols vary. Always verify current prescribing information, contraindications, and drug interactions using official local pharmacy databases (e.g., Lexicomp, Micromedex) or the manufacturer’s product insert before prescribing or administering medication.*
