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# Mefenamic Acid
## Overview
Mefenamic acid is a nonsteroidal anti-inflammatory drug (NSAID) used for the short-term relief of mild to moderate pain and for the management of primary dysmenorrhea. It is a weak acid with a pKa of 4.2.
## Primary Indications
* Pain (mild to moderate)
* Primary dysmenorrhea
## Adult Dosing
* **Pain:** 500 mg initially, then 250 mg every 6 hours as needed.
* **Primary Dysmenorrhea:** 500 mg initially, then 250 mg every 6 hours as needed, starting at the onset of pain or bleeding and continuing for up to 3 days.
* **Maximum daily dose:** 1500 mg.
* **Duration of therapy:** Not recommended for use for more than 7 days.
## Pediatric Dosing
* **Children 12 years and older:** Dosing is the same as for adults.
* **Children under 12 years:** Safety and efficacy have not been established.
## Dose Adjustments
* **Renal Impairment:** Use with caution. No specific dose adjustments are established, but it is generally avoided in severe renal impairment.
* **Hepatic Impairment:** Use with caution. No specific dose adjustments are established, but it is generally avoided in severe hepatic impairment.
* **Elderly:** Use with caution, as they are at increased risk for adverse effects.
## Contraindications
* Hypersensitivity to mefenamic acid or other NSAIDs.
* History of aspirin-induced asthma, urticaria, or allergic rhinitis.
* Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery.
* Active gastrointestinal bleeding or inflammatory bowel disease.
## Adverse Effects
* **Common:** Diarrhea, nausea, vomiting, abdominal pain, headache, dizziness, rash.
* **Serious:** Gastrointestinal bleeding, ulceration, perforation; cardiovascular thrombotic events (myocardial infarction, stroke); renal failure; hepatic failure; hypersensitivity reactions (including Stevens-Johnson syndrome and toxic epidermal necrolysis); exacerbation of asthma.
## Key Drug Interactions
* **Anticoagulants (e.g., warfarin):** Increased risk of bleeding. Monitor INR closely.
* **Corticosteroids:** Increased risk of gastrointestinal ulceration and bleeding.
* **Other NSAIDs and Aspirin:** Increased risk of gastrointestinal toxicity and additive effects.
* **Diuretics and Antihypertensives:** May decrease their efficacy and increase the risk of renal impairment.
* **Lithium:** Mefenamic acid can decrease lithium clearance, leading to increased lithium levels. Monitor lithium levels.
* **Methotrexate:** Mefenamic acid can increase methotrexate levels and toxicity.
## Monitoring
* Monitor for signs and symptoms of gastrointestinal bleeding (e.g., melena, hematemesis).
* Monitor renal function (e.g., serum creatinine, BUN) especially in patients with pre-existing renal disease, dehydration, or those taking concomitant nephrotoxic agents.
* Monitor liver function (e.g., ALT, AST) if signs of hepatic dysfunction develop.
* Monitor for cardiovascular risk factors and symptoms.
## Clinical Pearls
* Mefenamic acid should be taken with food or milk to minimize gastrointestinal upset.
* Due to its short half-life, it is typically dosed every 6 hours.
* It is generally not recommended for chronic pain management due to potential for serious side effects with prolonged use.
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**Disclaimer:** This information is intended for clinical use and is not a substitute for professional medical advice. Always consult the most current prescribing information and relevant guidelines before administering or recommending any medication. Dosing and recommendations may vary based on individual patient factors and local protocols.
