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# Mefenamic acid
## Overview
Mefenamic acid is an anthranilic acid derivative nonsteroidal anti-inflammatory drug (NSAID). It exhibits analgesic, anti-inflammatory, and antipyretic properties via non-selective inhibition of cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis.
## Primary Indications
* Treatment of mild to moderate pain.
* Management of primary dysmenorrhea.
* Off-label use: Rheumatoid arthritis, osteoarthritis (limited clinical utility compared to other NSAIDs).
## Adult Dosing
* **Pain/Dysmenorrhea:** 500 mg orally initially, followed by 250 mg every 6 hours as needed.
* **Duration:** Therapy should not exceed 7 days.
* **Maximum Dose:** Do not exceed 1,500 mg per day.
## Pediatric Dosing
* **Children >14 years:** Use adult dosing schedule.
* **Children <14 years:** Safety and efficacy have not been established. Use is generally not recommended in this population.
## Dose Adjustments
* **Renal Impairment:** Avoid in severe renal impairment (CrCl <30 mL/min). Use with caution in mild-to-moderate impairment; close monitoring of renal function is required.
* **Hepatic Impairment:** Use with caution. Consider lower doses if necessary; 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
* Known hypersensitivity (including aspirin or other NSAIDs).
* History of asthma, urticaria, or allergic-type reactions after aspirin/NSAID use.
* Active GI bleeding or peptic ulcer disease.
* Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery.
* Severe renal or hepatic failure.
* Third trimester of pregnancy (risk of premature closure of ductus arteriosus).
## Adverse Effects
* **Gastrointestinal:** Nausea, diarrhea (frequent), dyspepsia, abdominal pain, GI ulceration/bleeding.
* **Cardiovascular:** Hypertension, fluid retention, edema, increased risk of myocardial infarction or stroke.
* **Renal/Hepatic:** Elevated liver enzymes, interstitial nephritis, acute renal failure.
* **Hematologic:** Potential for inhibition of platelet aggregation.
## Key Drug Interactions
* **Anticoagulants (e.g., Warfarin):** Increased risk of bleeding.
* **ACE Inhibitors/ARBs/Diuretics:** Reduced antihypertensive effect and increased risk of acute kidney injury.
* **Lithium/Methotrexate:** Increased plasma concentrations and potential for toxicity due to reduced renal clearance.
* **Other NSAIDs/Corticosteroids:** Increased risk of GI ulceration and bleeding.
## Monitoring
* **Baseline/Periodic:** CBC, serum creatinine, BUN, and liver function tests.
* **Ongoing:** Monitor blood pressure, symptoms of GI bleeding (tarry stools), and signs of fluid retention.
## Clinical Pearls
* **Gastrointestinal Priority:** Mefenamic acid is known for a higher incidence of diarrhea compared to other NSAIDs; discontinue if diarrhea occurs.
* **Duration Limit:** Due to the risk of significant GI toxicity, clinical guidelines strictly recommend limiting therapy to 7 days.
* **Administration:** Take with food or milk to minimize gastric irritation.
* **Cardiovascular Warning:** Like all non-aspirin NSAIDs, it carries a boxed warning regarding cardiovascular thrombotic events.
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**Educational 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 before administering any medication.
