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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. It acts primarily by inhibiting the cyclooxygenase (COX-1 and COX-2) enzymes, leading to reduced prostaglandin synthesis.
## Primary Indications
* Treatment of primary dysmenorrhea.
* Treatment of mild-to-moderate pain.
* *Note: Use is generally limited to short-term therapy (≤7 days).*
## 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
* **Adolescents (≥14 years):** Follow adult dosing (500 mg initially, then 250 mg every 6 hours).
* **Children (<14 years):** Safety and efficacy have not been established. Not recommended for routine use.
## Dose Adjustments
* **Renal Impairment:** Avoid in patients with 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 signs of hepatic toxicity.
* **Geriatric:** Use the lowest effective dose for the shortest duration possible due to increased risk of GI, renal, and cardiovascular toxicity.
## Contraindications
* History of asthma, urticaria, or allergic-type reactions after taking aspirin or other NSAIDs.
* Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery.
* History of active peptic ulcer disease or gastrointestinal bleeding.
* Severe renal or hepatic impairment.
## Adverse Effects
* **Gastrointestinal:** Nausea, vomiting, diarrhea, abdominal pain, dyspepsia, peptic ulceration, GI bleeding.
* **Hematologic:** Anemia, leukopenia, thrombocytopenia.
* **Renal:** Fluid retention, edema, renal failure, interstitial nephritis.
* **Cardiovascular:** Hypertension, increased risk of thrombotic events (MI, stroke).
* **CNS:** Dizziness, headache, drowsiness.
## Key Drug Interactions
* **Anticoagulants (e.g., Warfarin):** Increased risk of bleeding.
* **Antiplatelet Agents/SSRIs:** Increased risk of GI bleeding.
* **ACE Inhibitors/ARBs/Diuretics:** Reduced antihypertensive effect; increased risk of acute renal failure.
* **Lithium/Methotrexate:** Decreased renal clearance, leading to increased toxicity.
## Monitoring
* **Baseline:** Renal function (BUN/SCr), CBC, and blood pressure.
* **Ongoing:** Monitor for signs of GI bleeding (occult blood, anemia), renal deterioration (edema, urine output), and cardiovascular symptoms. Periodically check LFTs if therapy is extended.
## Clinical Pearls
* **GI Protection:** Administer with food or milk to minimize gastric distress.
* **CV Risk:** All NSAIDs carry a boxed warning for increased risk of serious cardiovascular thrombotic events.
* **Diarrhea:** Mefenamic acid is uniquely more associated with diarrhea compared to other NSAIDs; if diarrhea occurs, discontinue the medication.
* **Pregnancy:** Avoid in the third trimester (≥30 weeks) due to the risk of premature closure of the fetal ductus arteriosus and oligohydramnios.
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**Educational Disclaimer:** This information is for educational purposes only. Clinical practice protocols vary by region and institution. Always verify dosages, contraindications, and drug interactions via current, institutional-approved drug references or clinical decision support tools before prescribing or administering medication.
