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# Mefenamic Acid
## Overview
Mefenamic acid is an anthranilic acid derivative nonsteroidal anti-inflammatory drug (NSAID). It exerts analgesic, anti-inflammatory, and antipyretic effects primarily by inhibiting cyclooxygenase (COX-1 and COX-2) enzymes, thereby reducing prostaglandin synthesis. It is typically intended for short-term use (≤7 days).
## Primary Indications
* Primary dysmenorrhea.
* Mild to moderate acute pain.
* Management of menorrhagia (off-label/specific formulations).
## Adult Dosing
* **Acute Pain/Dysmenorrhea:** 500 mg initial dose, followed by 250 mg every 6 hours as needed.
* **Maximum Dose:** Do not exceed 1,500 mg per day or 7 days of continuous treatment.
## Pediatric Dosing
* **Children ≥14 years:** Dosing is identical to the adult regimen (500 mg initial, then 250 mg every 6 hours).
* **Children <14 years:** Safety and efficacy have not been established. Use is generally not recommended unless directed by a specialist under specific institutional protocols.
## Dose Adjustments
* **Renal Impairment:** Use with caution in mild-to-moderate impairment. Mefenamic acid is contraindicated in severe renal impairment (CrCl <30 mL/min).
* **Hepatic Impairment:** Use with caution; monitor for increased drug exposure. Avoid in patients with active liver disease.
* **Elderly:** Use the lowest effective dose for the shortest duration due to increased risk of gastrointestinal (GI) toxicity and cardiovascular events.
## Contraindications
* Known hypersensitivity to mefenamic acid or other NSAIDs (including aspirin-induced asthma/urticaria).
* History of GI bleeding, ulceration, or perforation.
* Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery.
* Severe renal or hepatic failure.
* Third trimester of pregnancy (risk of premature closure of the ductus arteriosus).
## Adverse Effects
* **Common:** GI upset, nausea, diarrhea (frequent), dyspepsia, abdominal pain.
* **Serious:** GI bleeding/perforation, hypertension, edema, increased cardiovascular risk (MI/stroke), renal impairment, hepatotoxicity, and hematological abnormalities (anemia, leukopenia).
## Key Drug Interactions
* **Anticoagulants/Antiplatelets (e.g., Warfarin, Clopidogrel):** Increased risk of bleeding.
* **ACE Inhibitors/ARBs/Diuretics:** Reduced antihypertensive effect and increased risk of acute kidney injury.
* **Corticosteroids/SSRIs:** Increased risk of gastrointestinal ulceration.
* **Lithium/Methotrexate:** Decreased renal clearance, increasing the risk of toxicity.
## Monitoring
* Monitor GI symptoms (dark stools, abdominal pain).
* Assess blood pressure periodically during therapy.
* In long-term or high-risk patients: Monitor renal function (BUN/SCr) and liver function tests.
* Monitor CBC for signs of anemia or unusual bleeding.
## Clinical Pearls
* **GI Sensitivity:** Take with food or milk to minimize gastric irritation.
* **Short-term only:** This medication should not be used long-term due to non-selective COX inhibition which carries a significant risk of GI side effects.
* **Diarrhea:** Mefenamic acid is unique among many NSAIDs for its tendency to cause diarrhea; if it occurs, the medication should be discontinued.
* **Avoid Stacking:** Do not combine with other NSAIDs (e.g., ibuprofen, naproxen) simultaneously.
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**Educational Disclaimer:** This information is for educational purposes only. Clinical practices and dosing protocols may vary by region or institution. Always verify dosages, contraindications, and drug interactions against current, authoritative local prescribing references (e.g., BNF, local formulary, or package insert) before administration.
