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# Mefenamic acid
## Overview
Mefenamic acid is a nonsteroidal anti-inflammatory drug (NSAID) of the fenamate class. It possesses analgesic, anti-inflammatory, and antipyretic properties, primarily by inhibiting prostaglandin synthesis via cyclooxygenase (COX-1 and COX-2) inhibition.
## Primary Indications
* Treatment of mild to moderate pain.
* Primary dysmenorrhea.
## Adult Dosing
* **Initial Dose:** 500 mg orally.
* **Maintenance:** 250 mg orally every 6 hours as needed.
* **Maximum Duration:** Should generally not exceed 7 days of continuous therapy.
## Pediatric Dosing
* **Adolescents (≥14 years):** Same as adult dosing.
* **Children (<14 years):** Efficacy and safety 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 closely.
* **Hepatic Impairment:** Use with caution. Consider lower doses or avoiding in significant hepatic dysfunction due to increased risk of toxicity.
* **Elderly:** Use the lowest effective dose for the shortest duration due to increased risk of cardiovascular and gastrointestinal adverse events.
## Contraindications
* Known hypersensitivity to mefenamic acid or other NSAIDs/aspirin (risk of bronchospasm/anaphylaxis).
* History of asthma, urticaria, or allergic-type reactions after taking aspirin or other NSAIDs.
* Perioperative pain management in the setting of coronary artery bypass graft (CABG) surgery.
* Active peptic ulcer disease or gastrointestinal bleeding.
* Severe renal or hepatic failure.
## Adverse Effects
* **Gastrointestinal:** Nausea, diarrhea (often dose-limiting), abdominal pain, dyspepsia, peptic ulceration, GI bleeding.
* **Cardiovascular:** Increased risk of myocardial infarction, stroke, edema, and hypertension.
* **Renal:** Acute kidney injury, fluid retention, hyperkalemia.
* **Hematologic:** Anemia, blood dyscrasias.
* **Dermatologic:** Rash, pruritus, severe skin reactions (e.g., SJS/TEN).
## Key Drug Interactions
* **Anticoagulants (e.g., Warfarin):** Increased risk of bleeding.
* **Antiplatelets/SSRIs:** Increased risk of gastrointestinal bleeding.
* **Antihypertensives (ACE inhibitors, ARBs, Beta-blockers, Diuretics):** Reduced efficacy of antihypertensive agents; increased risk of nephrotoxicity.
* **Lithium/Methotrexate:** Decreased clearance, leading to potential toxicity.
* **Corticosteroids:** Increased risk of GI ulceration.
## Monitoring
* **Baseline/Intermittent:** Renal function (BUN/SCr), liver function tests, complete blood count (if long-term use).
* **Clinical:** Monitor for signs of GI bleeding (black stools, hematemesis), cardiovascular symptoms (chest pain, edema), and blood pressure control.
## Clinical Pearls
* **Gastrointestinal Profile:** Mefenamic acid is notably more likely to cause diarrhea than other NSAIDs. Discontinue if persistent diarrhea occurs.
* **Administration:** Take with food or milk to minimize gastrointestinal upset.
* **Cardiovascular Warning:** Like all NSAIDs, mefenamic acid carries a boxed warning regarding an increased risk of serious cardiovascular thrombotic events.
* **Pregnancy:** Avoid after 30 weeks gestation due to the risk of premature closure of the ductus arteriosus.
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**Educational Disclaimer:** This information is for educational purposes only. Clinical practice protocols vary by institution and region. Always consult the latest version of the manufacturer’s package insert, institutional guidelines, or a reliable clinical database (e.g., UpToDate, Lexicomp) before prescribing or administering medication.
