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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 by inhibiting cyclooxygenase (COX-1 and COX-2) enzymes, thereby reducing prostaglandin synthesis.
## Primary Indications
* Treatment of mild to moderate pain.
* Treatment of primary dysmenorrhea.
* Off-label: Management of heavy menstrual bleeding (menorrhagia).
## Adult Dosing
* **Acute Pain/Dysmenorrhea:** 500 mg initially, followed by 250 mg every 6 hours as needed.
* **Duration:** Therapy should not exceed 7 days.
## Pediatric Dosing
* **Age ≥14 years:** Follow adult dosing (500 mg initial, 250 mg every 6 hours).
* **Age <14 years:** Safety and efficacy have not been established. Use is generally not recommended.
## Dose Adjustments
* **Renal Impairment:** Avoid use in severe renal impairment (CrCl <30 mL/min). Use with caution and consider dose reduction for mild-to-moderate impairment.
* **Hepatic Impairment:** Use with caution; monitor for signs of hepatic toxicity.
* **Elderly:** Use the lowest effective dose for the shortest duration due to increased risk of cardiovascular and gastrointestinal complications.
## Contraindications
* Known hypersensitivity (including aspirin or other NSAID-induced asthma, urticaria, or allergic-type reactions).
* History of asthma induced by aspirin or NSAIDs.
* Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery.
* Active gastrointestinal (GI) ulceration or inflammatory bowel disease.
* Severe renal or hepatic failure.
* Third trimester of pregnancy (risk of premature closure of the ductus arteriosus).
## Adverse Effects
* **Gastrointestinal:** Abdominal pain, dyspepsia, diarrhea (frequent), nausea, GI ulceration, or bleeding.
* **Renal:** Fluid retention, edema, acute renal failure, interstitial nephritis.
* **Cardiovascular:** Hypertension, increased risk of myocardial infarction and stroke.
* **Hematologic:** Anemia, platelet aggregation inhibition.
* **Hepatic:** Elevated liver enzymes (rare but serious).
## Key Drug Interactions
* **Anticoagulants/Antiplatelets:** Increased risk of bleeding (e.g., warfarin, clopidogrel).
* **ACE Inhibitors/ARBs/Diuretics:** Reduced antihypertensive effect and increased risk of acute renal failure.
* **Lithium/Methotrexate:** Potential for decreased renal clearance leading to toxicity.
* **SSRIs:** Increased risk of upper GI bleeding.
* **Other NSAIDs/Corticosteroids:** Increased risk of GI toxicity.
## Monitoring
* **Baseline:** Renal function (BUN/SCr), CBC, and hepatic function in long-term therapy.
* **Ongoing:** Monitor blood pressure, symptoms of GI irritation, signs of occult bleeding (stools), and edema.
* **Renal:** Periodic monitoring of CrCl if long-term use is required.
## Clinical Pearls
* **Administration:** Take with food or milk to minimize gastrointestinal upset.
* **Duration:** Limit use beyond 7 days due to cumulative risk of toxicity, particularly diarrhea and GI ulceration.
* **Cardiovascular Warning:** Like all NSAIDs, mefenamic acid carries a boxed warning for potential increased risk of serious cardiovascular thrombotic events and serious gastrointestinal adverse events.
* **Diarrhea:** Mefenamic acid is uniquely associated with a higher incidence of diarrhea compared to other NSAIDs; if diarrhea occurs, the medication should be discontinued.
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**Disclaimer:** This information is for educational purposes only. Clinical practice guidelines vary by institution and region. Always verify specific dosing, safety profiles, and contraindications against current, official prescribing information (such as the FDA label or local formulary) before prescribing or administering medication.
