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# Mefenamic Acid
## Overview
Mefenamic acid is a nonsteroidal anti-inflammatory drug (NSAID) that exerts its effect primarily through the reversible inhibition of cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis. It is typically used for short-term management of pain due to its heightened risk of gastrointestinal and renal toxicity compared to other NSAIDs.
## Primary Indications
* Treatment of mild-to-moderate pain.
* Primary dysmenorrhea.
## Adult Dosing
* **Standard dose:** 500 mg orally initially, followed by 250 mg orally every 6 hours as needed.
* **Duration:** Therapy should not exceed 7 days.
## Pediatric Dosing
* **Children ≥14 years:** Dosing is identical to the adult regimen (500 mg load, then 250 mg every 6 hours).
* **Children <14 years:** Safety and efficacy have not been established; use is generally avoided.
## Dose Adjustments
* **Renal Impairment:** Avoid in patients with severe renal impairment (CrCl <30 mL/min). Dose cautiously in mild-to-moderate impairment.
* **Hepatic Impairment:** Use with caution; monitor for potential hepatotoxicity.
## Contraindications
* Known hypersensitivity to mefenamic acid or aspirin/other NSAIDs.
* History of asthma, urticaria, or allergic-type reactions after taking aspirin or other NSAIDs.
* Active peptic ulcer disease or gastrointestinal bleeding.
* Preoperative pain management in the setting of coronary artery bypass graft (CABG) surgery.
* Severe renal impairment.
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal pain, dyspepsia.
* **Serious:** GI bleeding, ulceration, perforation of the stomach or intestines, cardiovascular thrombotic events (myocardial infarction, stroke), renal impairment (interstitial nephritis, papillary necrosis), and anaphylactoid reactions.
* **Dermatologic:** Stevens-Johnson syndrome, toxic epidermal necrolysis (rare).
## Key Drug Interactions
* **Anticoagulants/Antiplatelets (e.g., Warfarin, Clopidogrel):** Increased risk of bleeding.
* **ACE Inhibitors/ARBs/Diuretics:** Reduced antihypertensive effect and increased risk of acute kidney injury.
* **Lithium:** May increase serum lithium levels, potentially leading to toxicity.
* **Methotrexate:** May increase methotrexate toxicity via decreased renal clearance.
## Monitoring
* **Baseline:** CBC, renal function (SCr/BUN), and liver function tests.
* **Periodic:** Monitor blood pressure, gastrointestinal symptoms, and signs of edema or weight gain. Monitor renal function if long-term use (within the 7-day limit) is required in elderly or comorbid patients.
## Clinical Pearls
* **Short-term use only:** Due to the risk of significant GI and renal adverse effects, use of mefenamic acid is strictly limited to a maximum of 7 days.
* **Administration:** Administer with food or milk to minimize gastrointestinal upset.
* **CV Risk:** All NSAIDs carry a boxed warning for increased risk of serious cardiovascular thrombotic events.
* **Pregnancy:** Avoid after 30 weeks of gestation (risk of premature closure of the ductus arteriosus).
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**Educational Disclaimer:** This information is for educational purposes only and does not constitute medical advice. Prescribing practices, local protocols, and clinical guidelines vary based on jurisdiction and patient-specific factors. Always verify current prescribing information in a trusted clinical resource (e.g., Lexicomp, UpToDate) before administering medication.
