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# Mefenamic Acid
## Overview
Mefenamic acid is a nonsteroidal anti-inflammatory drug (NSAID) belonging to the fenamate class. It is a weak acid with analgesic and anti-inflammatory properties, primarily through the inhibition of cyclooxygenase (COX) enzymes, thereby reducing prostaglandin synthesis.
## Primary Indications
* Short-term management of mild to moderate pain.
* Management of primary dysmenorrhea.
## Adult Dosing
* **Pain:** 500 mg every 6 hours as needed.
* **Dysmenorrhea:** 500 mg every 6 hours as needed, typically started at the onset of pain and bleeding and continued for up to 3 days.
* **Maximum Duration:** Should not be used for more than 7 days without medical supervision.
## Pediatric Dosing
* Mefenamic acid is generally not recommended for children under 14 years of age due to potential for adverse effects and lack of established safety and efficacy data.
## Dose Adjustments
* **Renal Impairment:** Use with caution. Dose reduction may be considered in severe impairment, but specific guidelines are lacking. Monitor renal function closely.
* **Hepatic Impairment:** Use with caution. Dose reduction may be considered in severe impairment, but specific guidelines are lacking. Monitor liver function closely.
## Contraindications
* Hypersensitivity to mefenamic acid or other NSAIDs.
* 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.
* Active gastrointestinal bleeding or ulceration.
* Severe renal or hepatic impairment.
* Third trimester of pregnancy.
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal pain, constipation, dyspepsia, rash.
* **Serious:** Gastrointestinal bleeding, ulceration, perforation; renal toxicity (acute kidney injury, interstitial nephritis); hepatotoxicity; cardiovascular thrombotic events (myocardial infarction, stroke); hypersensitivity reactions; Stevens-Johnson syndrome/toxic epidermal necrolysis.
## Key Drug Interactions
* **Anticoagulants (e.g., warfarin):** Increased risk of bleeding. Monitor INR closely.
* **Corticosteroids:** Increased risk of gastrointestinal bleeding and ulceration.
* **Selective Serotonin Reuptake Inhibitors (SSRIs):** Increased risk of gastrointestinal bleeding.
* **Diuretics and Antihypertensives (e.g., ACE inhibitors, ARBs, beta-blockers):** NSAIDs can reduce the efficacy of these agents and increase the risk of renal toxicity.
* **Lithium:** NSAIDs can increase serum lithium levels, potentially to toxic levels.
* **Methotrexate:** NSAIDs can increase methotrexate levels and toxicity.
* **Other NSAIDs and Aspirin:** Increased risk of adverse effects, particularly gastrointestinal.
## Monitoring
* **Gastrointestinal:** Signs and symptoms of bleeding (e.g., melena, hematemesis), abdominal pain.
* **Renal:** Renal function (serum creatinine, BUN) especially in patients with pre-existing renal disease or those on concomitant nephrotoxic agents.
* **Hepatic:** Liver function tests (ALT, AST) if signs of hepatic dysfunction develop.
* **Cardiovascular:** Monitor for signs of cardiovascular events.
* **Bleeding:** Platelet count and coagulation parameters if clinically indicated.
## Clinical Pearls
* Mefenamic acid should be taken with food or milk to minimize gastrointestinal upset.
* Due to the risk of gastrointestinal adverse effects, it should be used at the lowest effective dose for the shortest possible duration.
* Consider gastroprotective agents (e.g., PPIs) for patients at high risk of GI complications.
* Not recommended for use in inflammatory arthropathies where other NSAIDs are preferred.
* Onset of action for pain relief is typically within 1 hour.
**Disclaimer:** This information is intended for clinical use and does not replace professional medical advice. Always consult the most current prescribing information and relevant guidelines before making any treatment decisions.
