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# Mefenamic Acid
## Overview
Mefenamic acid is an anthranilic acid derivative nonsteroidal anti-inflammatory drug (NSAID). Like other NSAIDs, it inhibits cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis. It is distinguished by its short duration of therapy (typically limited to $\le$7 days).
## Primary Indications
* Treatment of primary dysmenorrhea.
* Short-term management of mild to moderate pain (typically $\leq$7 days).
## Adult Dosing
* **Dysmenorrhea/Pain:** 500 mg initially, followed by 250 mg every 6 hours as needed.
* **Maximum Duration:** Do not exceed 7 days of treatment.
## Pediatric Dosing
* **Adolescents ($\ge$14 years):** 500 mg initially, followed by 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 patients with severe renal impairment (CrCl <30 mL/min). Use with extreme caution in milder renal impairment; dose reduction may be necessary per institutional protocol.
* **Hepatic Impairment:** Use with caution. If required, use the lowest effective dose for the shortest duration.
## Contraindications
* Known hypersensitivity to mefenamic acid or aspirin/other NSAIDs.
* 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 peptic ulcer disease or gastrointestinal (GI) bleeding.
* Severe renal or hepatic impairment.
## Adverse Effects
* **Common:** GI distress (diarrhea, abdominal pain, nausea), dizziness, headache, edema.
* **Serious:** GI bleeding/ulceration, cardiovascular thrombotic events (myocardial infarction, stroke), hypertension, hepatotoxicity, acute renal failure, interstitial nephritis, hematologic abnormalities (e.g., hemolytic anemia with long-term use).
## Key Drug Interactions
* **Anticoagulants (e.g., Warfarin):** Increased risk of GI bleeding.
* **Antiplatelet agents/SSRIs:** Increased risk of bleeding.
* **Antihypertensives (ACE inhibitors/ARBs/Diuretics):** Potential reduction in antihypertensive efficacy and increased risk of acute kidney injury.
* **Lithium/Methotrexate:** Decreased clearance, increasing risk of toxicity.
* **Other NSAIDs:** Avoid concurrent use due to additive toxicity without added efficacy.
## Monitoring
* **Baseline:** Complete blood count (CBC), renal function (SCr/BUN), and liver function tests (LFTs) if used beyond an acute 7-day window.
* **Ongoing:** Monitor for occult blood loss (anemia), signs of GI bleeding (melena, hematemesis), blood pressure, and development of peripheral edema.
## Clinical Pearls
* **Duration:** Therapy is strictly limited to 7 days due to the increased risk of potentially fatal gastrointestinal toxicity and hematologic side effects.
* **Administration:** Take with food or milk to minimize gastric irritation.
* **Diarrhea:** Mefenamic acid is known to cause dose-related, sometimes severe, diarrhea; discontinue if this occurs.
* **CV Risk:** Like all NSAIDs, it carries a boxed warning regarding the increased risk of serious cardiovascular thrombotic events.
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**Educational Disclaimer:** This information is for educational purposes only and does not constitute medical advice. Clinical protocols vary by institution. Always verify dosages, contraindications, and drug interactions against current, authoritative local prescribing information or clinical decision support tools before prescribing or administering medication.
