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# Mefenamic Acid
## Overview
Mefenamic acid is a nonsteroidal anti-inflammatory drug (NSAID) of the fenamate class. It acts by inhibiting the cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis. Its pharmacological profile involves primarily analgesic and anti-inflammatory properties, but it is strictly limited in duration of use.
## 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:** Do not exceed 7 days of therapy.
* **Maximum Daily Dose:** 1,500 mg.
## Pediatric Dosing
* **Children ≥ 14 years:** Follow adult dosing guidelines.
* **Children < 14 years:** Safety and efficacy have not been established. Use is generally not recommended.
## Dose Adjustments
* **Renal Impairment:** Avoid use in patients with severe renal impairment (CrCl < 30 mL/min). Monitor closely in mild-to-moderate impairment.
* **Hepatic Impairment:** Use with caution; monitor for hepatotoxicity.
## Contraindications
* Known hypersensitivity (including aspirin or other NSAID-induced asthma, urticaria, or allergic-type reactions).
* History of GI bleeding or perforation related to previous NSAID therapy.
* Active peptic ulcer disease or inflammatory bowel disease.
* Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery.
* Severe renal or hepatic failure.
## Adverse Effects
* **GI:** Diarrhea (common and sometimes severe), nausea, abdominal pain, dyspepsia, peptic ulceration, GI bleeding.
* **CV:** Increased risk of serious cardiovascular thrombotic events (myocardial infarction, stroke).
* **Renal:** Fluid retention, edema, acute renal failure, interstitial nephritis.
* **Hematologic:** Anemia, leukopenia, thrombocytopenia.
* **Other:** Dizziness, headache, rash.
## Key Drug Interactions
* **Anticoagulants (e.g., Warfarin):** Increases risk of serious GI bleeding.
* **Antiplatelet agents/SSRIs:** Increases risk of GI bleeding.
* **ACE Inhibitors/ARBs/Diuretics:** Diminished antihypertensive effect and increased risk of renal impairment.
* **Lithium/Methotrexate:** Increases serum concentrations and toxicity risk due to reduced renal clearance.
* **Other NSAIDs:** Increased risk of adverse GI and renal effects; avoid co-administration.
## Monitoring
* **Renal Function:** Periodic BUN/Creatinine (especially in chronic or high-risk patients).
* **BP:** Monitor for increased blood pressure.
* **Signs of Toxicity:** Monitor for GI bleeding (melena, hematemesis), hepatotoxicity (jaundice, elevated LFTs), or fluid retention.
## Clinical Pearls
* **Diarrhea:** Mefenamic acid is uniquely associated with diarrhea at a higher frequency than other NSAIDs; discontinue immediately if severe.
* **Short Duration:** Because of the risk of severe diarrhea and other side effects, it is restricted to short-term, acute use (maximum 7 days).
* **Administration:** Administer with food or milk to reduce gastric irritation, though this may not mitigate all GI side effects.
* **CV Risk:** All NSAIDs (excluding aspirin) share a boxed warning for increased risk of cardiovascular thrombotic events. Always use the lowest effective dose for the shortest duration necessary.
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**Educational Disclaimer:** This information is for educational purposes only and does not constitute medical advice. Prescribing practices and local guidelines may vary. Always verify current prescribing information, contraindications, and drug interactions using official local drug monographs or institutional pharmacy protocols before initiating therapy.
