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# Mefenamic Acid
## Overview
Mefenamic acid is an anthranilic acid derivative nonsteroidal anti-inflammatory drug (NSAID). It exerts analgesic, anti-inflammatory, and antipyretic effects primarily through the inhibition of cyclooxygenase (COX-1 and COX-2) enzymes, which reduces prostaglandin synthesis.
## Primary Indications
* Treatment of mild to moderate pain.
* Management of primary dysmenorrhea.
## Adult Dosing
* **Pain/Dysmenorrhea:** 500 mg orally as an initial dose, followed by 250 mg every 6 hours as needed.
* **Maximum Duration:** Should not exceed 7 days of therapy.
## Pediatric Dosing
* **Children ≥14 years:** Use adult dosing (500 mg initial, then 250 mg every 6 hours).
* **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; monitor renal function closely.
* **Hepatic Impairment:** Use with caution. Since mefenamic acid is extensively metabolized by the liver, dose reduction or avoidance may be necessary in severe hepatic disease.
## Contraindications
* Known hypersensitivity to mefenamic acid, aspirin, or other NSAIDs (risk of cross-sensitivity).
* History of asthma, urticaria, or allergic-type reactions after taking aspirin or other NSAIDs.
* Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery.
* History of gastrointestinal (GI) bleeding or perforation related to previous NSAID therapy.
* Active peptic ulcer disease or inflammatory bowel disease.
* Severe renal or hepatic failure.
## Adverse Effects
* **GI:** Abdominal pain, diarrhea (common, often dose-related), nausea, dyspepsia, peptic ulceration, and GI hemorrhage.
* **Cardiovascular:** Increased risk of serious thrombotic events (myocardial infarction, stroke).
* **Renal:** Fluid retention, edema, acute renal failure, interstitial nephritis.
* **Hematologic:** Anemia, leukopenia, thrombocytopenia.
* **Dermatologic:** Skin rash, photosensitivity.
## Key Drug Interactions
* **Anticoagulants (e.g., Warfarin):** Increases risk of serious GI bleeding.
* **Antiplatelet agents/SSRIs:** Increases risk of GI bleeding.
* **Antihypertensives (ACE inhibitors, ARBs, Diuretics):** NSAIDs may blunt the antihypertensive effect and increase the risk of nephrotoxicity.
* **Lithium:** May increase serum lithium concentrations to toxic levels.
* **Methotrexate:** May increase the risk of methotrexate toxicity due to decreased renal clearance.
## Monitoring
* **Baseline:** Complete blood count (CBC), renal function (SCr/BUN), and hepatic function tests (LFTs).
* **Ongoing:** Periodic monitoring of renal function and blood pressure, especially in elderly or chronic users. Monitor for signs of GI bleeding (occult blood, anemia).
## Clinical Pearls
* **GI Sensitivity:** Mefenamic acid is notorious for inducing diarrhea; if diarrhea occurs, discontinue the drug.
* **NSAID Stewardship:** Use the lowest effective dose for the shortest duration possible to minimize cardiovascular and gastrointestinal risks.
* **Take with food:** Administer with food or milk to reduce gastrointestinal irritation.
* **Avoid in Elderly:** Generally avoided in geriatric patients due to increased risk of renal impairment and GI toxicity.
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**Disclaimer:** This information is for educational purposes only. Always consult current institutional protocols and the most recent package insert or clinical resources (such as Lexicomp or Micromedex) before prescribing or administering medication.
