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# Mefenamic Acid
## Overview
Mefenamic acid is a nonsteroidal anti-inflammatory drug (NSAID) of the fenamate class. It possesses analgesic, anti-inflammatory, and antipyretic properties, primarily by inhibiting cyclooxygenase (COX-1 and COX-2) enzymes, which reduces prostaglandin synthesis.
## Primary Indications
* Treatment of primary dysmenorrhea.
* Short-term management of mild to moderate pain (typically not exceeding 7 days of use).
## Adult Dosing
* **Dysmenorrhea/Pain:** 500 mg initially, followed by 250 mg every 6 hours as needed.
* **Maximum Duration:** Do not exceed 7 days of therapy.
## Pediatric Dosing
* **Children >14 years:** Dosing is identical to adult dosing (500 mg initial, then 250 mg q6h).
* **Children <14 years:** Safety and efficacy have not been established. Use is generally avoided.
## Dose Adjustments
* **Renal Impairment:** Use with caution. Avoid in severe renal impairment (CrCl <30 mL/min).
* **Hepatic Impairment:** Avoid in patients with severe hepatic impairment. Monitor closely for signs of hepatotoxicity.
## Contraindications
* Hypersensitivity to mefenamic acid, aspirin, or other NSAIDs.
* History of GI bleeding or perforation related to previous NSAID therapy.
* Active peptic ulcer disease or inflammatory bowel disease.
* Post-operative pain management in the setting of coronary artery bypass graft (CABG) surgery.
* Severe renal or hepatic failure.
* Third trimester of pregnancy (risk of premature closure of the ductus arteriosus).
## Adverse Effects
* **GI:** Diarrhea (common and dose-related), nausea, vomiting, abdominal pain, GI ulceration/bleeding.
* **Renal:** Fluid retention, edema, acute renal failure, interstitial nephritis.
* **Cardiovascular:** Increased risk of thrombotic events (myocardial infarction, stroke), hypertension.
* **Hematologic:** Anemia, pancytopenia (rare), inhibition of platelet aggregation.
* **CNS:** Dizziness, headache, nervousness.
## Key Drug Interactions
* **Anticoagulants (e.g., Warfarin):** Increased risk of bleeding.
* **Antiplatelet Agents (e.g., Aspirin, Clopidogrel):** Synergistic inhibition of platelets and increased GI risk.
* **ACE Inhibitors/ARBs/Diuretics:** Reduced antihypertensive effect; increased risk of nephrotoxicity.
* **Lithium:** May increase serum lithium levels, potentially leading to toxicity.
* **Methotrexate:** Increased risk of methotrexate toxicity due to reduced renal clearance.
## Monitoring
* Baseline and periodic CBC, serum creatinine, and BUN.
* Monitor blood pressure periodically.
* Assess for occult GI bleeding or signs of dyspepsia.
* Monitor for signs of fluid retention (edema, weight gain).
## Clinical Pearls
* **GI Caution:** The incidence of diarrhea is higher with mefenamic acid compared to other NSAIDs; discontinue if diarrhea occurs.
* **Duration:** Always use the lowest effective dose for the shortest duration necessary to achieve treatment goals.
* **Food:** Administer with food or milk if GI upset occurs.
* **Cardiovascular Warning:** Like all non-aspirin NSAIDs, mefenamic acid carries a boxed warning for an increased risk of serious cardiovascular thrombotic events.
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**Disclaimer:** This information is for educational purposes only. Drug dosing, contraindications, and interaction profiles can change; always verify current prescribing information via regional formularies, official package inserts, or clinical decision support tools before initiating therapy.
