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# Mefenamic Acid
## Overview
Mefenamic acid is a nonsteroidal anti-inflammatory drug (NSAID) belonging to the anthranilic acid derivative class. It has analgesic, anti-inflammatory, and antipyretic properties. Its mechanism of action involves 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, starting at the onset of pain or bleeding, whichever comes first.
* **Maximum:** Generally not to exceed 1500 mg in 24 hours, though some sources may cite up to 2000 mg in 24 hours for short-term use under medical supervision. Always adhere to the lowest effective dose and shortest duration.
## Pediatric Dosing
Mefenamic acid is generally **not recommended** for children under 14 years of age due to lack of established safety and efficacy data.
## Dose Adjustments
* **Renal Impairment:** Use with caution. Dose reduction may be necessary in severe impairment.
* **Hepatic Impairment:** Use with caution. Dose reduction may be necessary in severe impairment.
## Contraindications
* Known hypersensitivity to mefenamic acid or other NSAIDs.
* Patients with a history of bronchospasm, asthma, allergic rhinitis, or urticaria precipitated by aspirin or other NSAIDs.
* Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery.
* Inflammatory bowel disease.
* Third trimester of pregnancy.
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal pain, constipation, dyspepsia, rash, dizziness, headache, tinnitus.
* **Serious:**
* Gastrointestinal (GI) bleeding, ulceration, and perforation.
* Cardiovascular thrombotic events (MI, stroke).
* Renal toxicity (acute kidney injury, interstitial nephritis, papillary necrosis).
* Hepatotoxicity.
* Hypersensitivity reactions (including anaphylaxis).
* Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN).
* Exacerbation of asthma.
* Fluid retention and edema.
## Key Drug Interactions
* **Anticoagulants (e.g., warfarin):** Increased risk of bleeding.
* **Corticosteroids:** Increased risk of GI ulceration and bleeding.
* **Selective Serotonin Reuptake Inhibitors (SSRIs) / Serotonin-Norepinephrine Reuptake Inhibitors (SNRIs):** Increased risk of GI bleeding.
* **Other NSAIDs (including aspirin):** Increased risk of adverse effects, particularly GI toxicity.
* **Diuretics and Antihypertensives:** Reduced efficacy and increased risk of renal toxicity.
* **Lithium:** Increased lithium levels and toxicity.
* **Methotrexate:** Increased risk of methotrexate toxicity.
## Monitoring
* **Signs and symptoms of GI bleeding:** Melena, hematemesis, abdominal pain.
* **Renal function:** Serum creatinine, BUN.
* **Liver function:** Liver enzymes (ALT, AST).
* **Blood pressure:** Especially in patients with hypertension.
* **Signs of hypersensitivity reactions.**
## Clinical Pearls
* Administer with food or milk to minimize GI upset.
* Use the lowest effective dose for the shortest duration necessary to minimize risks.
* Avoid concurrent use with other NSAIDs.
* Discontinue immediately if signs of GI bleeding, renal toxicity, hepatotoxicity, or hypersensitivity occur.
* Consider gastroprotective agents (e.g., PPIs) in patients at high risk for GI events.
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*Disclaimer: This information is intended for clinical use and does not substitute for a thorough review of the complete prescribing information or local protocols. Always verify current product labeling and institutional guidelines before making prescribing decisions.*
