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# Mefenamic acid
## Overview
Mefenamic acid is an anthranilic acid derivative nonsteroidal anti-inflammatory drug (NSAID) that exhibits analgesic, anti-inflammatory, and antipyretic properties via the inhibition of cyclooxygenase (COX) enzymes, reducing prostaglandin synthesis. Its use is generally restricted to short-term therapy (≤7 days).
## Primary Indications
* Treatment of mild-to-moderate pain.
* Primary dysmenorrhea.
## Adult Dosing
* **Acute Pain/Dysmenorrhea:** 500 mg initially, followed by 250 mg every 6 hours as needed.
* **Maximum Duration:** 7 days.
## Pediatric Dosing
* **Ages ≥ 14 years:** Follow adult dosing.
* **Ages < 14 years:** Safety and efficacy have not been established; generally not recommended.
## Dose Adjustments
* **Renal Impairment:** Avoid in patients with severe renal impairment (CrCl < 30 mL/min). Use with caution and monitor closely in mild-to-moderate impairment.
* **Hepatic Impairment:** Use with caution; monitor liver enzymes. Avoid in severe hepatic impairment.
* **Geriatric:** Use the lowest effective dose for the shortest duration.
## Contraindications
* Known hypersensitivity to mefenamic acid or aspirin/NSAIDs (risk of bronchospasm or anaphylaxis).
* 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.
* Active peptic ulcer disease or gastrointestinal bleeding.
* Severe renal or hepatic failure.
## Adverse Effects
* **Common:** Abdominal pain, diarrhea, nausea, dizziness, headache.
* **Serious:** Gastrointestinal ulceration/perforation, myocardial infarction, stroke, new-onset or worsening hypertension, acute renal failure, fluid retention/edema, and hepatotoxicity.
## Key Drug Interactions
* **Anticoagulants (e.g., Warfarin):** Increased risk of bleeding.
* **Antiplatelet agents/SSRIs:** Increased risk of GI bleeding.
* **ACE Inhibitors/ARBs/Diuretics:** Reduced antihypertensive effect and increased risk of renal impairment.
* **Lithium/Methotrexate:** Decreased renal clearance, leading to potential toxicity.
## Monitoring
* **Baseline/Intermittent:** Renal function (BUN/SCr), liver function tests, CBC (for signs of occult bleeding).
* **Ongoing:** Blood pressure (especially in hypertensive patients) and signs of gastrointestinal distress or edema.
## Clinical Pearls
* **GI Protection:** Administer with food or milk to minimize gastrointestinal irritation.
* **CV Risk:** Use the lowest dose for the shortest possible duration, especially in patients with cardiovascular risk factors; NSAIDs are associated with an increased risk of serious cardiovascular thrombotic events.
* **Diarrhea:** Mefenamic acid is uniquely associated with persistent, sometimes severe, diarrhea; discontinue if this occurs.
* **Self-Limitation:** Due to toxicity (specifically GI and renal), it is not intended for chronic use.
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**Educational Disclaimer:** This information is for educational purposes only. Always verify current prescribing information, contraindications, and dosing guidelines via the manufacturer's official package insert, local institutional protocols, or reputable clinical databases (e.g., Lexicomp, UpToDate) before prescribing or administering medication.
