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# Mefenamic Acid
## Overview
Mefenamic acid is an anthranilic acid derivative nonsteroidal anti-inflammatory drug (NSAID). It exerts its effects primarily through the inhibition of cyclooxygenase (COX-1 and COX-2) enzymes, leading to reduced prostaglandin synthesis.
## Primary Indications
* Treatment of primary dysmenorrhea.
* Short-term management of mild to moderate pain (typically ≤7 days).
## Adult Dosing
* **Dysmenorrhea/Pain:** 500 mg orally as an initial dose, followed by 250 mg every 6 hours as needed.
* **Maximum Duration:** Do not exceed 7 days of continuous therapy.
## Pediatric Dosing
* **Adolescents (≥14 years):** Follow adult dosing schedule.
* **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; close monitoring is required, as NSAIDs can further reduce renal perfusion.
* **Hepatic Impairment:** Use with caution. If required, use the lowest effective dose for the shortest duration possible.
## Contraindications
* History of asthma, urticaria, or allergic-type reactions after taking aspirin or other NSAIDs.
* Hypersensitivity to mefenamic acid.
* Setting of coronary artery bypass graft (CABG) surgery.
* Active gastrointestinal (GI) bleeding or inflammatory bowel disease.
* Severe renal or hepatic failure.
## Adverse Effects
* **Gastrointestinal:** Diarrhea (common and potentially severe), nausea, abdominal pain, GI ulceration/perforation.
* **Cardiovascular:** Increased risk of myocardial infarction, stroke, and hypertension (Class effect).
* **Renal:** Fluid retention, edema, acute renal failure, interstitial nephritis.
* **Hematologic:** Anemia, thrombocytopenia, hemolytic anemia (with long-term use).
## Key Drug Interactions
* **Anticoagulants/Antiplatelets (e.g., Warfarin, Clopidogrel):** Increased risk of bleeding.
* **ACE Inhibitors/ARBs/Diuretics:** Reduced antihypertensive effect; increased risk of nephrotoxicity.
* **Lithium/Methotrexate:** Decreased renal clearance, leading to increased levels and potential toxicity.
* **Corticosteroids/SSRIs:** Increased risk of gastrointestinal ulceration/bleeding.
## Monitoring
* **Baseline/Intermittent:** CBC (hemoglobin/platelets), serum creatinine, BUN, and blood pressure.
* **Symptomatic:** Signs of GI occult bleeding (e.g., melena, hemoptysis), unexplained weight gain, or edema.
## Clinical Pearls
* **Diarrhea:** Mefenamic acid is uniquely associated with clinical diarrhea; discontinue if this occurs.
* **Shortest Duration:** Always use the lowest effective dose for the shortest period to minimize cardiovascular and gastrointestinal risks.
* **Administration:** Take with food or milk to minimize GI irritation.
* **Prostaglandin Inhibition:** Like other NSAIDs, it inhibits prostaglandin synthesis which may cause premature closure of the ductus arteriosus in late pregnancy; avoid in the third trimester.
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**Educational Disclaimer:** This information is for educational purposes only. Always consult the most recent product monograph, prescribing information, or your institutional clinical decision support tools before prescribing or administering medication. Verification of dosage, contraindications, and patient-specific factors is the responsibility of the licensed healthcare provider.
