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# Mefenamic Acid
## Overview
Mefenamic acid is an anthranilic acid derivative nonsteroidal anti-inflammatory drug (NSAID). It possesses analgesic, anti-inflammatory, and antipyretic properties, primarily by inhibiting cyclooxygenase (COX-1 and COX-2) enzymes, which reduces prostaglandin synthesis.
## Primary Indications
* Treatment of mild-to-moderate pain.
* Primary dysmenorrhea.
* *Note: Treatment duration should not exceed 7 days.*
## Adult Dosing
* **Pain/Dysmenorrhea:** 500 mg initially, followed by 250 mg every 6 hours as needed.
* **Maximum Dose:** 1,500 mg per day.
## Pediatric Dosing
* **Safety/Efficacy:** Not established for children under 14 years of age. Use is generally not recommended in pediatric populations due to limited safety data compared to other NSAIDs (e.g., ibuprofen).
## Dose Adjustments
* **Renal Impairment:** Avoid in severe renal impairment (CrCl < 30 mL/min). Use with caution and monitor closely if CrCl is 30–60 mL/min.
* **Hepatic Impairment:** Use with caution; monitor for increased risk of hepatotoxicity.
* **Geriatric Patients:** Use the lowest effective dose for the shortest duration due to increased risk of cardiovascular and gastrointestinal toxicities.
## Contraindications
* Known hypersensitivity to mefenamic acid or other NSAIDs (including aspirin-induced asthma/urticaria).
* History of asthma or bronchospasm related to NSAID use.
* History of gastrointestinal bleeding or peptic ulcer disease.
* Treatment of perioperative pain in the setting of coronary artery bypass graft (CABG) surgery.
* Severe renal or hepatic failure.
* Third trimester of pregnancy (risk of premature closure of the ductus arteriosus).
## Adverse Effects
* **Gastrointestinal:** Dyspepsia, nausea, diarrhea (frequent), abdominal pain, GI ulceration, or hemorrhage.
* **Cardiovascular:** Hypertension, fluid retention, increased risk of MI/stroke (class effect).
* **Renal:** Acute kidney injury, interstitial nephritis, fluid retention.
* **Hematologic:** Anemia, platelet inhibition.
* **CNS:** Dizziness, headache.
## Key Drug Interactions
* **Anticoagulants (e.g., Warfarin):** Increased risk of bleeding.
* **Antiplatelets (e.g., Clopidogrel, Aspirin):** Increased risk of GI toxicity and bleeding.
* **ACE Inhibitors/ARBs/Diuretics:** Reduced antihypertensive effect and potential for nephrotoxicity (the "triple whammy").
* **Lithium/Methotrexate:** Mefenamic acid may increase serum concentrations and toxicity of these drugs via reduced renal clearance.
* **Corticosteroids:** Increased risk of GI ulceration.
## Monitoring
* **Renal Function:** Monitor BUN, serum creatinine, and electrolytes periodically during long-term therapy.
* **GI:** Observe for signs of bleeding (melena, hematemesis).
* **Blood Pressure:** Monitor regularly, as NSAIDs can induce or worsen hypertension.
* **CBC:** Monitor if long-term therapy is required to screen for anemia or cytopenias.
## Clinical Pearls
* Diarrhea is a unique, dose-related adverse effect of mefenamic acid that may be severe; discontinue if it occurs.
* Take with food or milk to minimize gastrointestinal upset.
* Like other NSAIDs, it carries a Black Box Warning for increased risk of serious cardiovascular thrombotic events and serious gastrointestinal adverse events.
* Consult local hospital protocols, as hospital-specific guidelines may restrict use in favor of more established NSAIDs like naproxen or ibuprofen.
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**Educational Disclaimer:** This information is for educational purposes only. Always consult the latest manufacturer prescribing information, clinical guidelines, or a licensed pharmacist/physician before making prescribing or dosing decisions. Clinical settings may vary based on local protocols.
