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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 through the non-selective inhibition of cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis.
## Primary Indications
* Treatment of mild-to-moderate pain.
* Treatment of primary dysmenorrhea.
* *Note:* Use is generally limited to short-term therapy (not exceeding 7 days).
## Adult Dosing
* **Pain/Dysmenorrhea:** 500 mg orally as an initial dose, followed by 250 mg every 6 hours as needed.
* **Maximum Dose:** 1,500 mg per day.
## Pediatric Dosing
* **Children 14 years and older:** Same as adult dosing.
* **Children under 14 years:** Safety and efficacy are not established. Usage is generally avoided in this population.
## Dose Adjustments
* **Renal Impairment:** Avoid in severe renal impairment. Use with caution and monitor carefully in mild-to-moderate impairment.
* **Hepatic Impairment:** Use with caution; monitor liver enzymes. Dose reduction may be required.
* **Geriatric Patients:** Use the lowest effective dose for the shortest duration due to increased risk of gastrointestinal (GI) and renal adverse effects.
## Contraindications
* Known hypersensitivity to mefenamic acid or other NSAIDs (including aspirin-induced asthma/urticaria).
* History of GI bleeding or perforation related to previous NSAID therapy.
* Active peptic ulcer disease or inflammatory bowel disease.
* 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
* **GI:** Diarrhea (often dose-related), nausea, dyspepsia, abdominal pain, risk of GI ulceration/bleeding.
* **Renal/CV:** Fluid retention, edema, hypertension, elevated serum creatinine, potential increased risk of myocardial infarction or stroke.
* **Hematologic:** Anemia, rare cases of blood dyscrasias.
* **Neurologic:** Dizziness, headache, drowsiness.
## Key Drug Interactions
* **Anticoagulants (e.g., Warfarin):** Increased risk of bleeding.
* **Antiplatelet Agents/SSRIs:** Increased risk of GI bleeding.
* **ACE Inhibitors/ARBs/Diuretics:** Reduced efficacy for hypertension and increased risk of acute kidney injury.
* **Methotrexate:** Potential for increased methotrexate toxicity due to reduced renal clearance.
* **Lithium:** May increase serum lithium levels; monitor for toxicity.
## Monitoring
* Baseline and periodic monitoring of renal function (BUN/SCr) and liver function (AST/ALT/bilirubin).
* Periodic monitoring of blood pressure.
* Monitor for signs of GI bleeding (e.g., dark stools, coffee-ground emesis).
* Assess for occult blood loss during long-term therapy.
## Clinical Pearls
* Diarrhea is a hallmark side effect unique to mefenamic acid and may necessitate discontinuation of therapy.
* Due to the risk of severe GI, renal, and cardiovascular toxicity, mefenamic acid should be used at the lowest effective dose for the shortest duration possible consistent with individual patient treatment goals.
* Take with food or milk to minimize GI irritation, though it does not eliminate the risk of ulceration.
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**Educational Disclaimer:** This information is for educational purposes only. Clinical guidelines and local prescribing protocols vary. Always consult the latest PI (Prescribing Information) or institutional guidelines before dosing.
