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# Mefenamic Acid
## Overview
Mefenamic acid is an anthranilic acid derivative nonsteroidal anti-inflammatory drug (NSAID) that inhibits cyclooxygenase (COX-1 and COX-2) enzymes. It possesses analgesic, anti-inflammatory, and antipyretic properties.
## Primary Indications
* Treatment of mild to moderate pain.
* Primary dysmenorrhea.
## Adult Dosing
* **Initial Dose:** 500 mg orally.
* **Maintenance Dose:** 250 mg orally every 6 hours as needed.
* **Maximum Duration:** Usually limited to 1 week (7 days) due to risk of gastrointestinal and renal toxicity.
## Pediatric Dosing
* **Age ≥14 years:** Use adult dosing.
* **Age <14 years:** Safety and efficacy are not established. Use is generally avoided in favor of ibuprofen or naproxen.
## Dose Adjustments
* **Renal Impairment:** Avoid in severe renal impairment. Dose reduction may be required in moderate impairment; monitor closely.
* **Hepatic Impairment:** Use with caution. If required, use the lowest effective dose for the shortest duration.
* **Geriatric:** Increased risk of serious GI adverse events and renal impairment; use lowest effective dose.
## Contraindications
* Known hypersensitivity to mefenamic acid or other NSAIDs (including aspirin-induced asthma/urticaria).
* History of active peptic ulceration or chronic gastrointestinal inflammation.
* Treatment of perioperative pain in the setting of coronary artery bypass graft (CABG) surgery.
* Severe renal or hepatic impairment.
## Adverse Effects
* **Gastrointestinal:** Abdominal pain, diarrhea (common, can be severe), nausea, peptic ulceration, GI bleeding.
* **Renal:** Acute kidney injury, fluid retention, edema.
* **Cardiovascular:** Hypertension, potential increased risk of myocardial infarction and stroke (class effect).
* **Hematologic:** Anemia (due to occult blood loss), blood dyscrasias.
* **CNS:** Dizziness, headache, nervousness.
## Key Drug Interactions
* **Anticoagulants (e.g., Warfarin):** Increased risk of bleeding.
* **Antiplatelets/SSRIs:** Increased risk of GI bleeding.
* **ACE Inhibitors/ARBs/Diuretics:** Reduced antihypertensive effect and increased risk of renal impairment (nephrotoxicity).
* **Lithium/Methotrexate:** Potential increase in plasma concentrations, leading to toxicity.
## Monitoring
* **Baseline/Intermittent:** CBC, serum creatinine, BUN, and liver function tests.
* **General:** Monitor for signs of gastrointestinal bleeding (melena, hematemesis), changes in blood pressure, and peripheral edema.
## Clinical Pearls
* **Duration Limit:** Due to the risk of hemolytic anemia and severe GI effects with chronic use, therapy should not exceed 7 days.
* **Administration:** Administer with food or milk to minimize gastrointestinal distress.
* **Diarrhea:** Mefenamic acid-induced diarrhea is frequently dose-related and may require treatment discontinuation.
* **Cross-reactivity:** Use caution in patients with aspirin allergy due to potential cross-reactivity.
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*Disclaimer: This information is for educational purposes only. Always consult current institutional protocols and the most recent manufacturer prescribing information (package insert) before prescribing or administering medication.*
