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# Mefenamic Acid
## Overview
Mefenamic acid is an anthranilic acid derivative nonsteroidal anti-inflammatory drug (NSAID). It exhibits analgesic, anti-inflammatory, and antipyretic properties via non-selective inhibition of cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis.
## Primary Indications
* Treatment of mild to moderate pain (short-term use, typically ≤7 days).
* Primary dysmenorrhea.
## Adult Dosing
* **Initial Dose:** 500 mg orally.
* **Maintenance:** 250 mg orally every 6 hours as needed.
* **Maximum Duration:** Should not exceed 7 days of continuous therapy.
## 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 and monitor carefully in mild-to-moderate impairment.
* **Hepatic Impairment:** Use with caution. Consider dose reduction; avoid if severe impairment is present.
* **Elderly:** Use the lowest effective dose for the shortest duration due to increased risk of cardiovascular and gastrointestinal complications.
## Contraindications
* Known hypersensitivity to mefenamic acid or aspirin/NSAIDs.
* History of asthma, urticaria, or allergic-type reactions after taking aspirin or other NSAIDs.
* Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery.
* Active peptic ulceration or inflammatory bowel disease.
* Severe renal or hepatic failure.
* Third trimester of pregnancy (risk of premature closure of the ductus arteriosus).
## Adverse Effects
* **Gastrointestinal:** Nausea, vomiting, diarrhea (may be severe), abdominal pain, peptic ulcer, gastrointestinal bleeding.
* **Cardiovascular:** Hypertension, fluid retention, increased risk of MI or stroke (class effect).
* **Renal:** Acute kidney injury, interstitial nephritis, fluid retention/edema.
* **Hematologic:** Anemia, rare blood dyscrasias.
* **Hypersensitivity:** Rash, anaphylaxis.
## Key Drug Interactions
* **Anticoagulants/Antiplatelets (e.g., Warfarin, Clopidogrel):** Increased risk of hemorrhage.
* **ACE Inhibitors/ARBs/Diuretics:** Reduced antihypertensive effect and increased risk of acute renal failure.
* **Lithium:** May increase serum lithium levels, potentially leading to toxicity.
* **Methotrexate:** Increased risk of methotrexate toxicity due to reduced renal clearance.
* **Other NSAIDs:** Increased risk of side effects; avoid concurrent use.
## Monitoring
* Renal function (BUN/SCr) periodically during chronic or frequent use.
* Blood pressure monitoring.
* Signs and symptoms of GI bleeding (e.g., malaise, fatigue, anemia, melena).
* CBC and LFTs if therapy is extended (though therapy should not exceed 7 days).
## Clinical Pearls
* **Diarrhea:** Mefenamic acid is uniquely prone to causing severe diarrhea compared to other NSAIDs; if diarrhea occurs, the drug should be immediately discontinued.
* **Dosing Limits:** Strict adherence to the 7-day limit is required to minimize the risk of serious GI and renal adverse effects.
* **Administration:** Take with food or milk to minimize gastrointestinal upset.
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**Educational Disclaimer:** This information is for educational purposes and does not substitute for professional medical judgment. Always verify current prescribing information, institutional protocols, and patient-specific factors via official drug resources (e.g., FDA labels, BNF, or clinical pharmacists) before prescribing or administering medication.
