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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 the inhibition of cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis.
## Primary Indications
* Treatment of primary dysmenorrhea.
* Management of mild to moderate acute pain.
## Adult Dosing
* **Dysmenorrhea/Acute Pain:** 500 mg orally as an initial dose, followed by 250 mg every 6 hours as needed.
* **Maximum Duration:** Should not exceed 7 days of continuous therapy.
* **Maximum Dose:** 1,500 mg per day.
## Pediatric Dosing
* **Children ≥ 14 years:** Use adult dosing guidelines.
* **Children < 14 years:** Safety and efficacy have not been established. Use is generally not recommended in this population.
## Dose Adjustments
* **Renal Impairment:** Avoid in severe renal impairment (CrCl < 30 mL/min). Use with caution and monitor closely in mild to moderate impairment.
* **Hepatic Impairment:** Use with caution; monitor for signs of liver dysfunction. Consider dosage reduction or avoidance in severe impairment.
## Contraindications
* Known hypersensitivity to mefenamic acid or other NSAIDs (including aspirin-induced asthma/urticaria).
* History of asthma precipitated by aspirin or other NSAIDs.
* Active peptic ulceration or inflammatory bowel disease.
* Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery.
* Severe renal or hepatic impairment.
## Adverse Effects
* **Gastrointestinal:** Dyspepsia, nausea, abdominal pain, diarrhea (common and potentially severe), peptic ulceration, GI bleeding.
* **Renal:** Fluid retention, edema, acute renal failure, interstitial nephritis.
* **Cardiovascular:** Increased risk of thrombotic events (MI, stroke), hypertension.
* **Hematologic:** Anemia, thrombocytopenia, hemolytic anemia (with long-term use).
## Key Drug Interactions
* **Anticoagulants (e.g., Warfarin):** Increased risk of bleeding due to GI mucosal injury and antiplatelet effects.
* **Other NSAIDs/Aspirin:** Increased risk of GI toxicity and bleeding.
* **ACE Inhibitors/ARBs/Diuretics:** Reduced antihypertensive efficacy and increased risk of renal impairment (nephrotoxicity).
* **Lithium/Methotrexate:** Increased plasma concentrations and potential toxicity of these drugs due to reduced renal clearance.
## Monitoring
* Baseline and periodic renal function (SCr, BUN) and LFTs.
* Monitor for signs of GI bleeding (occult blood, anemia).
* Monitor blood pressure periodically.
* Assess for edema or unexpected weight gain.
## Clinical Pearls
* **Administration:** Take with food or milk to minimize gastrointestinal upset.
* **Duration:** Due to the risk of significant GI toxicity and diarrhea, therapy is strictly limited to short-term use (maximum 7 days).
* **Diarrhea:** Mefenamic acid is uniquely associated with severe, dose-related diarrhea; discontinue immediately if this occurs.
* **Cardiovascular Risk:** Like all NSAIDs, it carries a boxed warning for increased risk of serious cardiovascular thrombotic events.
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**Disclaimer:** This information is for educational purposes only. Drug information is subject to change based on evolving evidence and local institutional protocols. Always consult the latest package insert, the manufacturer’s clinical documentation, or a local formulary/pharmacist before prescribing or administering medication.
