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# Mefenamic Acid
## Overview
Mefenamic acid is an anthranilic acid derivative nonsteroidal anti-inflammatory drug (NSAID). It exerts analgesic, anti-inflammatory, and antipyretic effects primarily through the inhibition of cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis.
## Primary Indications
* Treatment of mild to moderate pain.
* Primary dysmenorrhea.
* Not indicated for long-term chronic treatment (limited to ≤7 days duration).
## Adult Dosing
* **Standard Dose:** 500 mg initially, followed by 250 mg every 6 hours as needed.
* **Maximum Dose:** Do not exceed 1,500 mg per day.
* **Duration:** Limit therapy to 7 days due to risk of gastrointestinal and renal toxicity.
## Pediatric Dosing
* **Children ≥14 years:** Use adult dosing (500 mg initial, 250 mg q6h; max 1,500 mg/day).
* **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). Use with caution in mild-to-moderate impairment.
* **Hepatic Impairment:** Use with caution; monitor for signs of hepatotoxicity.
## Contraindications
* Known hypersensitivity (including urticaria or asthma) to mefenamic acid, aspirin, or other NSAIDs.
* History of GI bleeding or active peptic ulcer disease.
* Setting of coronary artery bypass graft (CABG) surgery.
* Severe renal or hepatic impairment.
## Adverse Effects
* **Gastrointestinal:** Nausea, diarrhea (often dose-limiting), abdominal pain, GI ulceration/bleeding.
* **Cardiovascular:** Hypertension, edema, increased risk of myocardial infarction or stroke.
* **Renal/Hematologic:** Fluid retention, acute renal failure, hemolytic anemia (rare, with long-term use), agranulocytosis.
* **CNS:** Dizziness, headache, nervousness.
## Key Drug Interactions
* **Anticoagulants/Antiplatelets (e.g., Warfarin):** Increased risk of major bleeding.
* **Diuretics/ACE Inhibitors/ARBs:** Potential for diminished antihypertensive effect and increased risk of acute renal failure.
* **Lithium/Methotrexate:** NSAIDs can decrease renal clearance of these agents, leading to toxicity.
* **Corticosteroids/SSRIs:** Increased risk of gastrointestinal ulceration.
## Monitoring
* **Baseline:** CBC, serum creatinine, and LFTs if duration extends beyond short-term use.
* **Ongoing:** Blood pressure monitoring, signs of occult GI bleeding (stools), and renal function if patient is elderly or has comorbidities.
## Clinical Pearls
* **Diarrhea:** Mefenamic acid is uniquely associated with diarrhea, which may be severe; discontinue if it occurs.
* **Short-term Use:** Because of the high risk of GI and renal adverse events, it is strictly intended for short-term symptomatic relief.
* **Administration:** Administer with food or milk to decrease gastrointestinal upset.
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**Educational Disclaimer:** This information is for educational purposes only. Clinical practice protocols vary by institution and country. Always verify current prescribing information, contraindications, and drug interactions via official local drug databases or clinical resources before prescribing or administering medication.
