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# Mefenamic Acid
## Overview
Mefenamic acid is an anthranilic acid derivative NSAID that inhibits the cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis. It has analgesic, anti-inflammatory, and antipyretic properties. Use is generally restricted to short-term therapy (not exceeding 7 days).
## Primary Indications
* Treatment of mild to moderate pain.
* Management of primary dysmenorrhea.
## Adult Dosing
* **Pain/Dysmenorrhea:** 500 mg initially, followed by 250 mg every 6 hours as needed.
* **Maximum Dose:** Do not exceed 1,500 mg per 24 hours. Limit duration of therapy to 1 week.
## Pediatric Dosing
* **Children ≥ 14 years:** Same as adult dosing.
* **Children < 14 years:** Safety and efficacy are not established. Use is generally avoided.
## Dose Adjustments
* **Renal Impairment:** Use with caution. Not recommended in severe renal impairment (CrCl < 30 mL/min).
* **Hepatic Impairment:** Use with caution; may require dosage reduction in patients with mild to moderate hepatic impairment. Avoid in severe hepatic disease.
* **Geriatric:** Use the lowest effective dose for the shortest duration, as the risk of serious GI and renal adverse effects is elevated.
## Contraindications
* Known hypersensitivity to mefenamic acid or other NSAIDs (including aspirin-induced asthma or urticaria).
* History of GI bleeding or ulceration.
* Perioperative setting of coronary artery bypass graft (CABG) surgery.
* Severe renal or hepatic impairment.
* Third trimester of pregnancy (risk of premature closure of ductus arteriosus).
## Adverse Effects
* **Common:** Abdominal pain, nausea, diarrhea (frequent cause of discontinuation), constipation, dyspepsia.
* **Serious:** GI ulceration/perforation, myocardial infarction, stroke, fluid retention, hypertension, hepatotoxicity, acute renal failure, and hypersensitivity reactions (Stevens-Johnson syndrome).
## Key Drug Interactions
* **Anticoagulants/Antiplatelets (e.g., Warfarin, Clopidogrel):** Increased risk of major bleeding.
* **ACE Inhibitors/ARBs/Diuretics:** Reduced antihypertensive effect; increased risk of nephrotoxicity.
* **Lithium:** May increase serum lithium levels, leading to toxicity.
* **Methotrexate:** Increased risk of methotrexate toxicity due to reduced renal clearance.
* **SSRIs:** Increased risk of gastrointestinal bleeding.
## Monitoring
* **Baseline:** Serum creatinine, LFTs, CBC (if long-term/high-risk).
* **Periodic:** Blood pressure monitoring, signs of GI bleeding (anemia, melena), and renal function.
## Clinical Pearls
* **Formulation:** Taking with food or milk may reduce GI irritation but may delay onset of action.
* **GI Sensitivity:** Mefenamic acid is noted for a higher rate of diarrhea compared to other NSAIDs. Discontinue if persistent diarrhea occurs.
* **Prostaglandin inhibition:** Like all NSAIDs, it carries a Black Box Warning for increased risk of serious cardiovascular thrombotic events and gastrointestinal adverse events.
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**Educational Disclaimer:** This information is for educational purposes only. Clinical guidelines and prescribing information change frequently. Always consult the most current manufacturer labeling, institutional protocols, or a reliable clinical database (e.g., Lexicomp, UpToDate) before prescribing or administering medication.
