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# Mefenamic Acid
## Overview
Mefenamic acid is an anthranilic acid derivative nonsteroidal anti-inflammatory drug (NSAID). It exhibits analgesic, anti-inflammatory, and antipyretic properties by inhibiting cyclooxygenase (COX-1 and COX-2) enzymes, thereby reducing prostaglandin synthesis. Its use is generally limited to short-term therapy (up to 7 days).
## Primary Indications
* Treatment of mild to moderate pain.
* Primary dysmenorrhea.
## Adult Dosing
* **Acute Pain/Dysmenorrhea:** 500 mg orally initially, followed by 250 mg every 6 hours as needed.
* **Maximum Duration:** 7 days.
## Pediatric Dosing
* **Children ≥ 14 years:** Use adult dosing schedule.
* **Children < 14 years:** Safety and efficacy have not been established. Use is generally not recommended.
## Dose Adjustments
* **Renal Impairment:** Use with caution; avoid in severe renal impairment (CrCl < 30 mL/min).
* **Hepatic Impairment:** Use with caution; monitor for increased risk of hepatotoxicity. No specific dose reduction guidelines are standardized; clinical judgment is required.
* **Geriatric:** Use the lowest effective dose for the shortest duration due to increased risk of GI toxicity and renal impairment.
## Contraindications
* Known hypersensitivity to mefenamic acid or aspirin/NSAIDs.
* History of asthma, urticaria, or allergic-type reactions after taking aspirin or other NSAIDs (risk of anaphylaxis).
* Active peptic ulceration or inflammatory bowel disease.
* Treatment of perioperative pain in the setting of coronary artery bypass graft (CABG) surgery.
* Severe renal or hepatic impairment.
## Adverse Effects
* **Gastrointestinal:** Abdominal pain, diarrhea (may be severe), nausea, peptic ulcer, GI hemorrhage.
* **Cardiovascular:** Hypertension, edema, increased risk of cardiovascular thrombotic events (myocardial infarction/stroke).
* **Renal:** Acute kidney injury, interstitial nephritis, fluid retention.
* **Hematologic:** Anemia, blood dyscrasias.
* **Dermatologic:** Rash, Stevens-Johnson syndrome (rare).
## Key Drug Interactions
* **Anticoagulants (e.g., Warfarin):** Increases risk of bleeding.
* **Antiplatelet agents/SSRIs:** Increased risk of GI bleeding.
* **Antihypertensives (ACE inhibitors, ARBs, Beta-blockers, Diuretics):** Reduced efficacy of antihypertensives and increased risk of nephrotoxicity.
* **Lithium/Methotrexate:** May increase serum concentrations and toxicity.
* **Corticosteroids:** Increased risk of GI ulceration.
## Monitoring
* **Baseline/Periodic:** Renal function (BUN/SCr), CBC, and liver function tests (LFTs) for long-term use.
* **Chronic:** Monitor blood pressure and signs of GI bleeding or edema.
## Clinical Pearls
* **GI Sensitivity:** Mefenamic acid is known to cause diarrhea more frequently than other NSAIDs; discontinue if diarrhea occurs.
* **Black Box Warning:** As with all NSAIDs, it carries a warning regarding increased risk of serious cardiovascular thrombotic events and serious gastrointestinal adverse events, including bleeding, ulceration, and perforation.
* **Administration:** Take with food or milk to minimize gastrointestinal irritation.
* **Off-label:** Sometimes used in pediatric populations for juvenile rheumatoid arthritis, but dosing is provider-dependent and lacks robust regulatory approval.
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**Educational Disclaimer:** This information is for educational purposes only. Clinical practice protocols vary by institution and region. Always verify specific dosing, safety guidelines, and contraindications via current local prescribing information (e.g., FDA-approved product labeling or the British National Formulary) before administration.
