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# Mefenamic Acid
## Overview
Mefenamic acid is an anthranilic acid derivative nonsteroidal anti-inflammatory drug (NSAID) that exhibits analgesic, anti-inflammatory, and antipyretic properties. Like other NSAIDs, it inhibits cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis.
## Primary Indications
* Treatment of mild to moderate pain.
* Treatment of primary dysmenorrhea.
## Adult Dosing
* **Pain/Dysmenorrhea:** 500 mg orally as an initial dose, followed by 250 mg every 6 hours as needed.
* **Maximum Duration:** Should not exceed 7 days of treatment.
## Pediatric Dosing
* **Children ≥ 14 years:** Use adult dosing regimen.
* **Children < 14 years:** Safety and efficacy have not been established. Use is generally not recommended.
## Dose Adjustments
* **Renal Impairment:** Use with caution. Avoid in patients with severe renal impairment (CrCl < 30 mL/min).
* **Hepatic Impairment:** Reduce dose or avoid in patients with severe hepatic impairment.
## Contraindications
* Hypersensitivity to mefenamic acid or any component of the formulation.
* History of asthma, urticaria, or allergic-type reactions after taking aspirin or other NSAIDs.
* Treatment of perioperative pain in the setting of coronary artery bypass graft (CABG) surgery.
* Active GI bleeding or peptic ulcer disease.
* Severe renal or hepatic failure.
## Adverse Effects
* **Gastrointestinal:** Nausea, abdominal pain, diarrhea (may be severe), constipation, GI ulceration/bleeding.
* **Neurological:** Headache, dizziness, nervousness.
* **Renal:** Fluid retention, edema, potential for acute renal failure.
* **Hematologic:** Anemia, hemagglutination inhibition.
* **Serious:** Cardiovascular thrombotic events, myocardial infarction, stroke, skin reactions (Stevens-Johnson syndrome).
## Key Drug Interactions
* **Anticoagulants (e.g., Warfarin):** Increases risk of serious GI bleeding.
* **ACE Inhibitors/ARBs/Diuretics:** Reduced antihypertensive effect and increased risk of acute renal failure.
* **Lithium:** May increase serum lithium concentrations to toxic levels.
* **Methotrexate:** Increases risk of methotrexate toxicity via reduced renal clearance.
* **Other NSAIDs/Aspirin:** Increased risk of GI toxicity and adverse cardiovascular effects.
## Monitoring
* **Baseline/Periodic:** Renal function (creatinine, BUN), liver function tests, complete blood count (if long-term/chronic use).
* **Clinical:** Monitor for signs of GI bleeding (melena, hematemesis), fluid retention, weight gain, or elevated blood pressure.
## Clinical Pearls
* **GI Toxicity:** Mefenamic acid is associated with a higher incidence of diarrhea compared to other NSAIDs; if severe diarrhea occurs, discontinue therapy.
* **Cardiovascular Warning:** Like all non-aspirin NSAIDs, it carries a boxed warning regarding the increased risk of serious cardiovascular thrombotic events.
* **Administration:** Take with food or milk to minimize gastrointestinal upset.
* **Pregnancy:** Avoid after 30 weeks gestation due to the risk of premature closure of the ductus arteriosus.
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*Disclaimer: This information is for educational purposes and does not replace professional medical judgment. Always consult the latest prescribing information, local clinical guidelines, or a pharmacist to verify specific dosing and safety protocols before prescribing or administering medication.*
