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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 inhibition of cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis.
## Primary Indications
* Primary dysmenorrhea.
* Mild to moderate pain (short-term use, generally ≤7 days).
## Adult Dosing
* **Standard:** 500 mg initially, followed by 250 mg every 6 hours as needed.
* **Maximum:** Do not exceed 1,500 mg per day. Treatment duration should be limited to 7 days or fewer.
## Pediatric Dosing
* **Adolescents (≥14 years):** Follow adult dosing: 500 mg initially, then 250 mg every 6 hours as needed.
* **Children (<14 years):** Safety and efficacy have not been established. Use is generally not recommended.
## Dose Adjustments
* **Renal Impairment:** Avoid in severe renal impairment. Use with caution and monitor carefully in mild-to-moderate impairment; reduced dosing may be required.
* **Hepatic Impairment:** Use with caution; monitor for elevated liver enzymes. Avoid in severe hepatic impairment.
* **Geriatric:** Use the lowest effective dose for the shortest duration due to increased risk of gastrointestinal (GI) toxicity and renal insufficiency.
## Contraindications
* 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.
* History of asthma or bronchospasm precipitated by aspirin or other NSAIDs.
* Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery.
* Severe renal or hepatic failure.
## Adverse Effects
* **Common:** GI disturbances (nausea, vomiting, diarrhea, abdominal pain/dyspepsia).
* **Serious:** GI ulceration/perforation, cardiovascular thrombotic events (myocardial infarction or stroke), hypertension, fluid retention/edema, renal impairment, and hepatotoxicity.
* **Hematologic:** May cause reversible anemia or prolonged bleeding time due to inhibition of platelet aggregation.
## 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 acute kidney injury.
* **Lithium/Methotrexate:** Potential for increased serum concentrations and toxicity.
* **Corticosteroids:** Increased risk of GI ulceration.
## Monitoring
* **Renal Function:** Monitor serum creatinine and BUN in patients with risk factors.
* **GI:** Monitor for signs of occult blood loss or anemia.
* **Blood Pressure:** Regular monitoring, especially in patients with hypertension.
* **Liver Function:** Periodic monitoring if long-term therapy is considered (though long-term use is not indicated).
## Clinical Pearls
* **Short Duration:** FDA labeling strictly limits therapy to 7 days due to the high incidence of GI-related adverse effects compared to other NSAIDs.
* **NSAID Sensitivity:** Patients with "ASA triad" (asthma, nasal polyps, ASA sensitivity) are at higher risk for severe reactions.
* **Take with food:** Administering with food or milk may reduce GI irritation.
* **Cardiovascular Warning:** Like all non-aspirin NSAIDs, mefenamic acid carries a Black Box Warning for an increased risk of serious cardiovascular thrombotic events.
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**Educational Disclaimer:** This information is for educational purposes only. Drug dosing, contraindications, and interaction profiles can change. Always verify current prescribing information using institutional protocols, the package insert, or professional resources like Micromedex or Lexicomp before making clinical decisions.
