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# Mefenamic Acid
## Overview
Mefenamic acid is a nonsteroidal anti-inflammatory drug (NSAID) that exerts an analgesic and anti-inflammatory effect through the inhibition of cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis. It is typically limited to short-term use (≤7 days).
## Primary Indications
* Treatment of mild to moderate pain.
* Treatment of primary dysmenorrhea.
## Adult Dosing
* **Mild to Moderate 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 treatment.
## Pediatric Dosing
* **Adolescents ≥ 14 years:** Same as adult dosing.
* **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 extreme caution in mild-to-moderate impairment; close monitoring of renal function is required.
* **Hepatic Impairment:** Use with caution; may require dose reduction. Avoid in severe hepatic impairment.
* **Geriatric:** Use the lowest effective dose for the shortest duration due to increased risk of GI bleeding and cardiovascular events.
## Contraindications
* Known hypersensitivity to mefenamic acid or other NSAIDs (including aspirin-induced asthma/urticaria).
* History of asthma or bronchospasm associated with NSAIDs.
* Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery.
* History of active gastrointestinal (GI) ulceration or inflammatory bowel disease.
* Severe renal or hepatic failure.
## Adverse Effects
* **Gastrointestinal:** Nausea, abdominal pain, diarrhea (may be severe), dyspepsia, occult blood loss, GI ulceration/perforation.
* **Cardiovascular:** Hypertension, edema, increased risk of myocardial infarction or stroke.
* **Renal:** Acute renal failure, interstitial nephritis, fluid retention.
* **Hematologic:** Anemia, platelet inhibition (less pronounced than aspirin).
* **CNS:** Headache, dizziness, drowsiness.
## Key Drug Interactions
* **Anticoagulants (e.g., Warfarin):** Increased risk of major bleeding complications.
* **Antiplatelet Agents/SSRIs:** Increased risk of GI bleeding.
* **Antihypertensives (ACE inhibitors, ARBs, diuretics):** Diminished antihypertensive effect; increased risk of nephrotoxicity.
* **Lithium/Methotrexate:** NSAIDs can decrease renal clearance of these drugs, leading to increased plasma concentrations and toxicity.
## Monitoring
* Baseline and periodic CBC, renal function (serum creatinine/BUN), and liver enzymes.
* Monitor blood pressure during initial treatment.
* Observe for signs or symptoms of GI bleeding (e.g., melena, hematemesis).
## Clinical Pearls
* **Diarrhea:** Mefenamic acid is uniquely associated with the potential for severe diarrhea; discontinue immediately if this occurs.
* **Take with food:** Administer with food or milk to minimize gastrointestinal upset.
* **CV Risk:** All NSAIDs carry a boxed warning for increased risk of serious cardiovascular thrombotic events and gastrointestinal toxicity (bleeding, ulcerations, perforation).
* **Short-term only:** This medication is not indicated for chronic pain due to the cumulative risk of toxicity.
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**Disclaimer:** This information is for educational purposes only. Clinical practice protocols vary. Always verify current prescribing information, contraindications, and drug interactions using official databases (e.g., FDA labels, regional formularies) before prescribing or administering medication.
