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# Mefenamic Acid
## Overview
Mefenamic acid is an anthranilic acid derivative, nonsteroidal anti-inflammatory drug (NSAID). It exerts anti-inflammatory, analgesic, and antipyretic effects primarily through non-selective inhibition of cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis.
## Primary Indications
* Treatment of mild to moderate pain.
* Primary dysmenorrhea.
* Note: Use is generally limited to short-term therapy (not exceeding 7 days).
## Adult Dosing
* **Standard dose:** 500 mg initially, followed by 250 mg every 6 hours as needed.
* **Maximum daily dose:** 1,500 mg/day.
## Pediatric Dosing
* **Children ≥14 years:** Dosing is identical to adult dosing.
* **Children <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; monitor renal function closely.
* **Hepatic Impairment:** Use with caution. Monitor for signs of hepatic toxicity.
## 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.
* Third trimester of pregnancy.
## Adverse Effects
* **Gastrointestinal:** Nausea, vomiting, diarrhea (often dose-limiting), abdominal pain, GI ulceration/bleeding.
* **Cardiovascular:** Hypertension, edema, increased risk of thrombotic events (MI, stroke).
* **Renal:** Acute kidney injury, interstitial nephritis, fluid retention.
* **Hematologic:** Anemia, platelet inhibition.
* **Other:** Dizziness, headache, rash.
## Key Drug Interactions
* **Anticoagulants/Antiplatelets (e.g., Warfarin, Clopidogrel):** Increased risk of bleeding.
* **ACE Inhibitors/ARBs/Diuretics:** Reduced antihypertensive effect and increased risk of acute kidney injury.
* **Lithium/Methotrexate:** Decreased renal clearance, leading to potential toxicity.
* **Corticosteroids/SSRIs:** Increased risk of gastrointestinal ulceration.
## Monitoring
* **Renal:** Baseline and periodic serum creatinine/BUN, especially in elderly or comorbid patients.
* **GI:** Monitor for occult blood or symptomatic bleeding (melena, hematemesis).
* **Cardiovascular:** Monitor blood pressure.
* **Hepatic:** Monitor liver function tests if symptomatic.
## Clinical Pearls
* **Duration:** Therapy should be limited to the shortest duration possible to control symptoms, as long-term use is associated with a higher incidence of gastrointestinal and cardiovascular adverse effects.
* **Administration:** Administer with food or milk to minimize GI irritation.
* **Diarrhea:** Mefenamic acid is uniquely associated with severe diarrhea compared to other NSAIDs; discontinue if diarrhea occurs.
* **Local Protocol:** Always verify institutional guidelines, as preferred NSAID selection may vary based on local formulary and safety guidelines.
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**Disclaimer:** This information is for educational purposes only. Drug dosing, contraindications, and interaction profiles are subject to change. Always verify current prescribing information using official drug labels (e.g., FDA labels) or institutional clinical decision support tools before prescribing or administering medication.
