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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.
* Primary dysmenorrhea.
* *Off-label:* Management of menorrhagia.
## Adult Dosing
* **Acute Pain/Dysmenorrhea:** 500 mg initially, followed by 250 mg every 6 hours as needed.
* **Maximum Duration:** Should not exceed 7 days of therapy.
## Pediatric Dosing
* **Children ≥ 14 years:** Same as adult dosing (500 mg initial, then 250 mg every 6 hours as needed).
* **Children < 14 years:** Safety and efficacy have not been established. Use is generally not recommended.
## Dose Adjustments
* **Renal Impairment:** Avoid in severe renal impairment (CrCl < 30 mL/min). Use with caution in mild-to-moderate impairment; monitor renal function closely.
* **Hepatic Impairment:** Use with caution; monitor for elevated liver enzymes. Dose reduction may be necessary in patients with hepatic impairment.
## Contraindications
* Known hypersensitivity to mefenamic acid, aspirin, or other NSAIDs.
* History of asthma, urticaria, or allergic-type reactions after taking aspirin or other NSAIDs.
* Active peptic ulceration or inflammatory bowel disease.
* Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery.
* Severe renal or hepatic failure.
## Adverse Effects
* **Gastrointestinal:** Nausea, diarrhea (often dose-related), abdominal pain, GI ulceration or bleeding.
* **Renal:** Fluid retention, edema, acute renal failure, interstitial nephritis.
* **Cardiovascular:** Increased risk of myocardial infarction or stroke (class effect).
* **Hematologic:** Anemia, thrombocytopenia, leukopenia.
* **Neurologic:** Dizziness, headache, drowsiness.
## Key Drug Interactions
* **Anticoagulants (e.g., Warfarin):** Increased risk of bleeding; monitor INR.
* **Antiplatelet agents/SSRIs:** Increased risk of GI bleeding.
* **Antihypertensives (ACE inhibitors, ARBs, Beta-blockers, Diuretics):** Reduced efficacy of antihypertensive therapy and increased risk of nephrotoxicity.
* **Methotrexate/Lithium:** Reduced renal clearance, increasing the risk of toxicity.
## Monitoring
* **GI:** Monitor for signs of occult blood loss or GI perforation.
* **Renal:** Periodically check serum creatinine, BUN, and electrolytes during long-term use.
* **Blood Pressure:** Monitor closely at the start of therapy.
* **CBC:** Monitor if long-term treatment is required to assess for anemia or blood dyscrasias.
## Clinical Pearls
* **Diarrhea:** Mefenamic acid is uniquely associated with dose-related diarrhea; if diarrhea occurs, the dose should be reduced or the drug discontinued.
* **Duration:** Efficacy is highest when started at the onset of pain or menses; limited to short-term use (≤ 7 days) to minimize GI and renal risks.
* **Avoidance:** Similar to other NSAIDs, it should be avoided in the third trimester of pregnancy due to the risk of premature closure of the ductus arteriosus.
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**Educational Disclaimer:** This information is for educational purposes only. Clinical practice protocols vary by institution and region. Always verify specific dosages, contraindications, and updated safety warnings against the most current FDA-approved prescribing information or institutional clinical guidelines before prescribing or administering medication.
