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# Mefenamic acid
## Overview
Mefenamic acid is an anthranilic acid derivative, nonsteroidal anti-inflammatory drug (NSAID). It exerts anti-inflammatory, analgesic, and antipyretic effects primarily by inhibiting cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis.
## Primary Indications
* Treatment of primary dysmenorrhea.
* Management of mild to moderate pain.
* *Note:* Short-term use (usually $\leq$ 7 days).
## Adult Dosing
* **Pain/Dysmenorrhea:** 500 mg initially, followed by 250 mg every 6 hours as needed.
* **Maximum Dose:** 1,500 mg per day.
## Pediatric Dosing
* **Age $\geq$ 14 years:** Same as adult dosing.
* **Age < 14 years:** Safety and efficacy have not been established; use is generally avoided.
## Dose Adjustments
* **Renal Impairment:** Avoid in patients with advanced renal disease. Use with extreme caution in mild-to-moderate impairment; close monitoring of renal function is required.
* **Hepatic Impairment:** Reduce dose or avoid in patients with hepatic impairment due to risk of hepatotoxicity.
## Contraindications
* Known hypersensitivity (including aspirin-induced asthma, urticaria, or allergic-type reactions).
* History of asthma or bronchospasm related to NSAIDs.
* Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery.
* Active peptic ulcer disease or GI bleeding.
* Severe renal or hepatic failure.
* Third trimester of pregnancy (risk of premature closure of the ductus arteriosus).
## Adverse Effects
* **Common:** Abdominal pain, diarrhea (can be severe), nausea, dyspepsia, dizziness, nervousness.
* **Serious:** GI bleeding, ulceration, perforation, myocardial infarction, stroke, renal failure, hypertension, fluid retention, hepatotoxicity, and anaphylaxis.
## Key Drug Interactions
* **Anticoagulants (e.g., Warfarin):** Increased risk of bleeding.
* **ACE Inhibitors/ARBs/Diuretics:** Reduced antihypertensive effect and increased risk of acute kidney injury.
* **Lithium/Methotrexate:** Decreased renal clearance, leading to elevated, potentially toxic serum levels.
* **Other NSAIDs/Corticosteroids:** Increased risk of GI toxicity.
## Monitoring
* **Baseline/Intermittent:** Serum creatinine, BUN, liver function tests, complete blood count (CBC).
* **Clinical:** Monitor for signs of GI bleeding (melena, hematemesis), persistent hypertension, peripheral edema, or cardiovascular symptoms.
## Clinical Pearls
* **Diarrhea:** Mefenamic acid is uniquely associated with the development of severe diarrhea. If diarrhea occurs, the drug should be discontinued immediately.
* **Duration:** Limit total duration of therapy to less than one week to minimize the risk of GI and renal complications.
* **Administration:** Administer with food or milk to minimize gastrointestinal irritation.
* **CV Risk:** Like all non-aspirin NSAIDs, it carries a boxed warning for increased risk of serious cardiovascular thrombotic events and gastrointestinal toxicity.
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**Educational Disclaimer:** This information is for educational purposes only and does not constitute medical advice. Dosing and clinical practices may vary by local institutional protocols. Always consult the most current product monograph or prescribing information (e.g., DailyMed or manufacturer labeling) before finalizing a prescription.
