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# Mefenamic Acid
## Overview
Mefenamic acid is an anthranilic acid derivative nonsteroidal anti-inflammatory drug (NSAID) that exhibits analgesic, anti-inflammatory, and antipyretic properties. Like other NSAIDs, it inhibits cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis.
## Primary Indications
* Treatment of mild to moderate pain.
* Treatment of primary dysmenorrhea.
## Adult Dosing
* **Mild to Moderate Pain / Dysmenorrhea:** 500 mg initially, followed by 250 mg every 6 hours as needed.
* **Duration:** Therapy should not exceed 1 week.
## Pediatric Dosing
* **Safety/Efficacy:** Not established for children younger than 14 years.
* **Adolescents (≥14 years):** Follow adult dosing: 500 mg initial dose, followed by 250 mg every 6 hours as needed.
## Dose Adjustments
* **Renal Impairment:** Avoid in severe renal impairment. Use with caution in mild-to-moderate impairment; monitor for fluid retention and renal function decline.
* **Hepatic Impairment:** Avoid in severe hepatic impairment. Mefenamic acid is extensively metabolized by the liver; use with caution in patients with hepatic disease.
## Contraindications
* Known hypersensitivity to mefenamic acid or other NSAIDs (including aspirin-induced asthma or urticaria).
* 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:** Abdominal pain, diarrhea (common), nausea, dyspepsia, elevated liver enzymes, GI bleeding/ulceration.
* **Cardiovascular:** Fluid retention, edema, hypertension, increased risk of thrombotic events (myocardial infarction, stroke).
* **Renal:** Acute renal failure, interstitial nephritis, hyperkalemia.
* **Hematologic:** Anemia, blood dyscrasias.
* **Dermatologic:** Skin rash, photosensitivity.
## Key Drug Interactions
* **Anticoagulants (e.g., Warfarin):** Increased risk of bleeding.
* **Antiplatelet Agents/SSRIs:** Increased risk of GI bleeding.
* **ACE Inhibitors/ARBs/Diuretics:** Reduced antihypertensive effect and increased risk of acute kidney injury.
* **Lithium/Methotrexate:** Potential for increased plasma concentrations and toxicity.
## Monitoring
* Baseline and periodic assessment of renal function (BUN/SCr) and liver enzymes.
* Blood pressure monitoring, especially in patients with hypertension.
* Hemoglobin/Hematocrit if long-term therapy is considered (though long-term use is not advised).
* Monitor for signs of GI toxicity (e.g., melena, hematemesis).
## Clinical Pearls
* **Duration Limit:** Due to the risk of significant GI side effects (particularly diarrhea) and renal issues, treatment is strictly limited to 7 days.
* **GI Sensitivity:** Mefenamic acid is associated with a higher incidence of diarrhea compared to other NSAIDs.
* **CV Risk:** All NSAIDs, including mefenamic acid, carry a boxed warning for increased risk of serious cardiovascular thrombotic events and serious gastrointestinal adverse events.
* **Administration:** Administer with food or milk to minimize gastrointestinal upset.
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**Educational Disclaimer:** This information is for educational purposes only. Clinical guidelines and local protocols vary. Verify all dosing, contraindications, and drug interactions with the most current primary literature or institutional pharmacy resources before prescribing or administering medication.
