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# Mefenamic Acid
## Overview
Mefenamic acid is an anthranilic acid derivative nonsteroidal anti-inflammatory drug (NSAID) that inhibits cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis. It possesses analgesic, anti-inflammatory, and antipyretic properties.
## Primary Indications
* Treatment of primary dysmenorrhea.
* Treatment of mild to moderate pain (short-term use, typically ≤7 days).
## Adult Dosing
* **Dysmenorrhea/Pain:** 500 mg initially, followed by 250 mg every 6 hours as needed.
* **Maximum Duration:** 7 days.
* **Maximum Dose:** 1500 mg per day.
## Pediatric Dosing
* **Children ≥14 years:** Use adult dosing as listed above.
* **Children <14 years:** Safety and efficacy have not been established. Not recommended.
## Dose Adjustments
* **Renal Impairment:** Avoid in severe renal impairment (CrCl <30 mL/min). Use with caution in mild-to-moderate impairment; monitor renal function closely.
* **Hepatic Impairment:** Use with caution. Monitor for signs of hepatotoxicity; avoid in severe hepatic impairment.
* **Geriatric:** Use the lowest effective dose for the shortest duration due to increased risk of cardiovascular and gastrointestinal (GI) toxicity.
## Contraindications
* Known hypersensitivity (including aspirin-induced asthma or urticaria).
* History of asthma induced by NSAIDs.
* Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery.
* Active peptic ulceration or chronic inflammation of the GI tract.
* Severe renal or hepatic failure.
## Adverse Effects
* **GI:** Abdominal pain, diarrhea (common, dose-related), nausea, dyspepsia, peptic ulceration, GI bleeding.
* **Renal:** Fluid retention, edema, renal failure, interstitial nephritis.
* **Cardiovascular:** Hypertension, increased risk of myocardial infarction or stroke (class effect).
* **Hematologic:** Anemia, blood dyscrasias.
* **Other:** Dizziness, headache, skin rash.
## Key Drug Interactions
* **Anticoagulants (e.g., Warfarin):** Increased risk of bleeding; monitor INR.
* **ACE Inhibitors/ARBs/Diuretics:** Reduced antihypertensive effect; increased risk of acute kidney injury.
* **Aspirin/Other NSAIDs:** Increased risk of GI toxicity and bleeding; additive effects.
* **Lithium:** May increase serum lithium concentrations to toxic levels.
* **Methotrexate:** May increase methotrexate toxicity via decreased renal clearance.
## Monitoring
* **Blood Pressure:** Monitor periodically during therapy.
* **Renal Function:** Serum creatinine and electrolytes if long-term use is required (though not indicated).
* **GI Symptoms:** Monitor for signs of occult blood loss, melena, or epigastric pain.
* **Hepatotoxicity:** Periodic liver function tests (LFTs) if prolonged use occurs.
## Clinical Pearls
* **Administration:** Take with food or milk to minimize potential GI upset.
* **Diarrhea:** Mefenamic acid is uniquely associated with dose-related diarrhea; discontinue if this occurs.
* **Short-Term Limit:** Due to the risk profile (particularly GI and renal), therapy is strictly limited to 7 days.
* **Cardiovascular Warning:** Like all NSAIDs, it carries a boxed warning regarding serious cardiovascular thrombotic events and GI risks.
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*Disclaimer: This information is for educational purposes only. Clinical practice guidelines vary by region and institution. Always verify dosages, contraindications, and drug interactions against the most current institutional protocols and the manufacturer’s package insert before prescribing.*
