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# Mefenamic Acid
## Overview
Mefenamic acid is an anthranilic acid derivative nonsteroidal anti-inflammatory drug (NSAID). Like other NSAIDs, it inhibits cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis. It is distinguished by a shorter approved duration of therapy (limited to 7 days).
## Primary Indications
* Treatment of mild to moderate pain.
* Treatment of primary dysmenorrhea.
## Adult Dosing
* **Initial Dose:** 500 mg orally.
* **Maintenance Dose:** 250 mg orally every 6 hours as needed.
* **Maximum Duration:** 7 days.
## Pediatric Dosing
* **Children >14 years:** Follow 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.
* **Hepatic Impairment:** Use with caution; monitor for signs of hepatic toxicity.
## Contraindications
* Known hypersensitivity to mefenamic acid or components.
* History of asthma, urticaria, or allergic-type reactions after taking aspirin or other NSAIDs.
* Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery.
* Active peptic ulceration or inflammatory bowel disease.
## Adverse Effects
* **Gastrointestinal:** Diarrhea (common), nausea, abdominal pain, GI ulceration, or bleeding.
* **Hematologic:** Anemia, leukopenia, thrombocytopenia.
* **Renal:** Edema, acute renal failure, interstitial nephritis.
* **Cardiovascular:** Increased risk of thrombotic events, myocardial infarction, and stroke.
## Key Drug Interactions
* **Anticoagulants (e.g., Warfarin):** Increased risk of bleeding.
* **ACE Inhibitors/ARBs/Diuretics:** May diminish the antihypertensive effect and increase risk of nephrotoxicity.
* **Methotrexate:** Increased risk of methotrexate toxicity due to reduced renal clearance.
* **Lithium:** May increase lithium serum concentrations.
* **Aspirin/Other NSAIDs:** Increased risk of GI adverse effects and bleeding; avoid concomitant use.
## Monitoring
* **GI:** Monitor for signs of bleeding (occult blood, anemia).
* **Renal:** Monitor serum creatinine and BUN, especially in high-risk patients.
* **Blood Pressure:** Regular monitoring during therapy.
* **Duration:** Ensure therapy does not exceed 7 days.
## Clinical Pearls
* **Diarrhea:** Mefenamic acid is uniquely associated with the development of severe diarrhea. If diarrhea occurs, the drug should be discontinued immediately and typically should not be resumed.
* **Administration:** Take with food or milk to minimize gastrointestinal upset.
* **NSAID Warning:** All NSAIDs share a boxed warning regarding serious cardiovascular thrombotic events and serious gastrointestinal adverse events (bleeding, ulceration, and perforation).
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*Disclaimer: This information is for educational purposes and does not replace professional clinical judgment. Always verify current prescribing information, institutional protocols, and patient-specific factors via reliable clinical databases (e.g., Lexicomp, UpToDate) before prescribing or administering medication.*
