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# Mefenamic Acid
## Overview
Mefenamic acid is an anthranilic acid derivative nonsteroidal anti-inflammatory drug (NSAID). It exerts anti-inflammatory, analgesic, 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.
* Primary dysmenorrhea.
* *Note: Duration of therapy should not exceed 7 days.*
## Adult Dosing
* **Initial Dose:** 500 mg orally.
* **Maintenance:** 250 mg orally every 6 hours as needed.
* **Maximum Dose:** 1,500 mg/day (limited to 7 days of treatment).
## Pediatric Dosing
* **Children > 14 years:** Follow adult dosing.
* **Children < 14 years:** Safety and efficacy have not been established. Use is generally avoided due to lack of clinical data.
## Dose Adjustments
* **Renal Impairment:** Avoid in patients with severe renal impairment (CrCl < 30 mL/min). Clinical guidelines vary; use with extreme caution in mild-to-moderate impairment, monitor renal function closely.
* **Hepatic Impairment:** Use with caution; monitor for signs of hepatic toxicity. Avoid in severe hepatic impairment.
* **Geriatric:** Use the lowest effective dose for the shortest duration due to increased risk of gastrointestinal (GI) and renal complications.
## Contraindications
* Known hypersensitivity to mefenamic acid or aspirin/other NSAIDs.
* 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 history of severe GI bleeding.
* Severe renal or hepatic failure.
## Adverse Effects
* **GI:** Diarrhea (common and potentially severe), nausea, abdominal pain, dyspepsia.
* **Renal:** Fluid retention, edema, elevated serum creatinine, acute renal failure.
* **Hematologic:** Increased risk of bleeding, anemia, leukopenia.
* **Cardiovascular:** Increased risk of myocardial infarction and stroke (class effect).
* **CNS:** Dizziness, headache, nervousness.
## Key Drug Interactions
* **Anticoagulants (e.g., Warfarin):** Increased risk of major bleeding.
* **Antiplatelets (e.g., Aspirin, Clopidogrel):** Increased GI toxicity and bleeding risk.
* **Antihypertensives (ACE inhibitors/ARBs/Diuretics):** Potential reduction in antihypertensive effect and increased risk of acute kidney injury.
* **Lithium:** May increase serum lithium levels, leading to toxicity.
* **Methotrexate:** Increased risk of methotrexate toxicity due to reduced renal excretion.
## Monitoring
* **Baseline:** CBC, renal function (SCr, BUN), and hepatic function tests.
* **Ongoing:** Monitor for GI symptoms (melena, hematemesis), blood pressure, peripheral edema, and signs of skin rash.
## Clinical Pearls
* **Diarrhea:** Mefenamic acid is uniquely associated with the development of severe diarrhea. If diarrhea occurs, the drug should be discontinued immediately.
* **GI Protection:** Consider a proton pump inhibitor (PPI) if the patient is at high risk for GI ulceration.
* **Duration:** The 7-day restriction on duration is critical due to the increased risk of dose-related adverse events.
* **Administration:** Take with food or milk to minimize gastric irritation.
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**Educational Disclaimer:** This information is for educational purposes for healthcare professionals. Clinical practice guidelines and prescribing information can vary by region and institution. Always verify current prescribing information, package inserts, and local protocols before initiating therapy.
