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# Mefenamic Acid
## Overview
Mefenamic acid is a nonsteroidal anti-inflammatory drug (NSAID) of the fenamate class. It acts primarily by inhibiting the cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis. Its primary use is in the management of mild to moderate pain and primary dysmenorrhea. Treatment duration is limited to no more than 7 days.
## Primary Indications
* Primary dysmenorrhea.
* Treatment of mild to moderate pain (short-term, ≤7 days).
## Adult Dosing
* **Dysmenorrhea/Pain:** 500 mg initially, followed by 250 mg every 6 hours as needed.
* **Maximum Dose:** Do not exceed 1.5 grams (1500 mg) per 24 hours.
## Pediatric Dosing
* **Adolescents (≥14 years):** Same as adult dosing.
* **Children (<14 years):** Safety and efficacy are not 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 renal function.
* **Hepatic Impairment:** Use with caution; monitor for signs of liver dysfunction. Dose reduction may be required.
* **Elderly:** Use the lowest effective dose for the shortest duration due to increased risk of serious cardiovascular and gastrointestinal events.
## Contraindications
* History of asthma, urticaria, or allergic-type reactions to aspirin or other NSAIDs.
* Perioperative setting of coronary artery bypass graft (CABG) surgery.
* Active peptic ulcer disease or gastrointestinal (GI) bleeding.
* Severe renal, hepatic, or cardiac failure.
* Third trimester of pregnancy (risk of premature closure of ductus arteriosus).
## Adverse Effects
* **GI:** Nausea, diarrhea (frequent), abdominal pain, GI ulceration/perforation.
* **Cardiovascular:** Hypertension, edema, increased risk of MI or stroke (Black Box Warning).
* **Renal:** Acute kidney injury, fluid retention.
* **Hematologic:** Anemia, platelet aggregation inhibition.
* **CNS:** 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 antihypertensive effect and increased risk of renal impairment.
* **Lithium/Methotrexate:** Potential for increased serum concentrations and toxicity.
## Monitoring
* **Renal Function:** Monitor BUN/Creatinine periodically in chronic or high-risk patients.
* **Blood Pressure:** Monitor regularly during initiation/dose changes.
* **GI:** Monitor for occult blood loss or symptoms of GI ulceration.
* **CBC:** Monitor if using for prolonged periods (rarely indicated).
## Clinical Pearls
* **Administration:** Take with food or milk to minimize GI irritation.
* **Duration:** Strict adherence to the 7-day maximum duration is critical to minimize the risk of serious adverse effects.
* **Diarrhea:** Mefenamic acid is notably more likely to cause diarrhea compared to other NSAIDs.
* **Not for Routine Use:** Due to its side effect profile, it is generally considered a second- or third-line NSAID for mild pain when other options are ineffective or contraindicated.
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**Educational Disclaimer:** This information is for educational purposes only. Clinical practice protocols may vary by institution. Always verify dosages, contraindications, and drug interactions against current, official prescribing information (e.g., FDA-approved labeling or local formulary guidelines) before prescribing or administering medication.
