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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.
## Primary Indications
* Treatment of mild to moderate pain.
* Primary dysmenorrhea.
* *Off-label:* Heavy menstrual bleeding (menorrhagia).
## Adult Dosing
* **Pain/Dysmenorrhea:** 500 mg orally initially, followed by 250 mg every 6 hours as needed.
* **Maximum Duration:** Should not exceed 7 days of treatment.
## Pediatric Dosing
* **Safety/Efficacy:** Not established for children under 14 years of age.
## Dose Adjustments
* **Renal Impairment:** Use with extreme caution in patients with moderate to severe renal impairment. Avoid if creatinine clearance (CrCl) is < 30 mL/min.
* **Hepatic Impairment:** Use with caution; dose reduction may be necessary. Monitor liver function closely.
* **Geriatrics:** Dose adjustments are often required due to increased risk of gastrointestinal toxicity and renal complications. Use the lowest effective dose for the shortest duration.
## Contraindications
* Known hypersensitivity to mefenamic acid or other NSAIDs (including aspirin-induced asthma/urticaria).
* History of active gastrointestinal (GI) ulceration or inflammatory bowel disease.
* Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery.
* Severe renal or hepatic impairment.
## Adverse Effects
* **Gastrointestinal:** Nausea, abdominal pain, diarrhea (specifically associated with mefenamic acid), GI bleeding, ulceration.
* **Cardiovascular:** Increased risk of thrombotic events (myocardial infarction, stroke), hypertension, edema.
* **Renal:** Acute renal failure, fluid retention, interstitial nephritis.
* **Hematologic:** Anemia, blood dyscrasias, prolonged bleeding time.
## Key Drug Interactions
* **Anticoagulants (e.g., Warfarin):** Increased risk of bleeding.
* **Corticosteroids/SSRIs:** Increased risk of GI ulceration or bleeding.
* **Antihypertensives (ACE inhibitors, ARBs, Diuretics):** Reduced efficacy and increased risk of acute kidney injury.
* **Lithium/Methotrexate:** Decreased renal clearance, leading to potential toxicity.
## Monitoring
* **Baseline/Periodic:** Renal function (BUN/SCr), CBC (hemoglobin/platelets), blood pressure, and liver function tests.
* **Clinical:** Monitor for signs of GI bleeding (melena, hematemesis), persistent abdominal pain, or peripheral edema.
## Clinical Pearls
* **GI Profile:** Diarrhea is the most distinct gastrointestinal side effect compared to other NSAIDs; it may be dose-dependent and can require discontinuation.
* **Cardiovascular Warning:** Mefenamic acid carries the standard "black box" warning for increased risk of serious cardiovascular thrombotic events and gastrointestinal toxicity common to all non-aspirin NSAIDs.
* **Administration:** Take with food or milk to minimize gastrointestinal upset.
* **Efficacy:** If therapeutic response is not seen within 7 days, reassess the diagnosis.
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**Educational Disclaimer:** This information is for educational purposes and does not constitute medical advice or a substitute for professional clinical judgment. Always verify dosages and contraindications against the current package insert or local drug formularies, as prescribing guidelines may vary by region and clinical context.
