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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.
* Treatment of primary dysmenorrhea.
## Adult Dosing
* **Pain/Dysmenorrhea:** 500 mg orally initially, followed by 250 mg every 6 hours as needed.
* **Maximum Duration:** Should not exceed 7 days of continuous therapy.
## Pediatric Dosing
* **Children ≥ 14 years:** Use adult dosing schedule.
* **Children < 14 years:** Safety and efficacy have not been established. Use is generally discouraged.
## 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:** Avoid in patients with severe hepatic impairment.
## Contraindications
* Known hypersensitivity to mefenamic acid, aspirin, or other NSAIDs (risk of anaphylaxis/angioedema).
* 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 ulcer disease or inflammatory bowel disease.
## Adverse Effects
* **Gastrointestinal:** Nausea, vomiting, diarrhea (may be severe), abdominal pain, GI ulceration/bleeding.
* **Renal:** Fluid retention, edema, acute renal failure, interstitial nephritis.
* **Cardiovascular:** Hypertension, increased risk of serious thrombotic events (MI, stroke).
* **Hematologic:** Anemia, blood dyscrasias, prolonged bleeding time.
* **CNS:** Dizziness, headache, drowsiness.
## Key Drug Interactions
* **Anticoagulants (e.g., Warfarin):** Increased risk of bleeding due to antiplatelet effects and GI mucosal damage.
* **ACE Inhibitors/ARBs/Diuretics:** Reduced antihypertensive effect; increased risk of nephrotoxicity.
* **Lithium/Methotrexate:** NSAIDs may decrease renal clearance, leading to potential toxicity.
* **Other NSAIDs/Corticosteroids:** Increased risk of GI ulceration and hemorrhage.
## Monitoring
* Baseline and periodic CBC, BMP (serum creatinine, electrolytes).
* Monitor blood pressure periodically.
* Assess for signs of occult GI bleeding (tarry stools, anemia) and hepatotoxicity.
## Clinical Pearls
* **GI Sensitivity:** Mefenamic acid has a significantly higher incidence of gastrointestinal side effects (especially diarrhea) compared to other NSAIDs.
* **Black Box Warning:** NSAIDs increase the risk of serious CV thrombotic events and serious GI adverse events, including bleeding, ulceration, and perforation.
* **Administration:** Administer with food or milk to minimize GI upset.
* **Efficacy:** If therapeutic response is not seen within 2–3 days, re-evaluate the diagnosis.
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**Educational Disclaimer:** This information is for educational purposes only. Drug dosing, contraindications, and interaction profiles can change. Always verify current prescribing information using institutional protocols, reliable drug databases (e.g., Lexicomp, Micromedex), or the manufacturer’s package insert before prescribing or administering medication.
