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# Mefenamic Acid
## Overview
Mefenamic acid is a nonsteroidal anti-inflammatory drug (NSAID) belonging to the fenamate class. It possesses analgesic, anti-inflammatory, and antipyretic properties through the inhibition of cyclooxygenase (COX) enzymes, thereby reducing prostaglandin synthesis.
## Primary Indications
* Mild to moderate pain, particularly associated with dysmenorrhea.
* Rheumatoid arthritis and osteoarthritis (less commonly used for chronic inflammatory conditions due to GI risks).
## 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 or bleeding.
* **Maximum Daily Dose:** 1500 mg. Treatment duration should not exceed 7 days for pain.
## Pediatric Dosing
* Mefenamic acid is generally **not recommended** for use in children under 12 years of age due to limited safety and efficacy data.
## Dose Adjustments
* **Renal Impairment:** Use with caution. Dose reduction may be necessary in patients with severe renal impairment.
* **Hepatic Impairment:** Use with caution. Dose reduction may be necessary in patients with severe hepatic impairment.
## Contraindications
* Known 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 history of recurrent gastrointestinal ulceration or bleeding.
* Severe heart failure.
* Severe renal impairment.
* Severe hepatic impairment.
* Third trimester of pregnancy.
## Adverse Effects
* **Common:** Diarrhea, nausea, vomiting, abdominal pain, dyspepsia, constipation, rash, dizziness, headache.
* **Serious:** Gastrointestinal bleeding, ulceration, and perforation; renal toxicity (including interstitial nephritis and papillary necrosis); hepatic dysfunction; cardiovascular thrombotic events (MI, stroke); hypersensitivity reactions; bronchospasm (especially in aspirin-sensitive 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 (including aspirin):** Increased risk of gastrointestinal toxicity and potential for reduced efficacy of low-dose aspirin for cardioprotection.
* **Diuretics and Antihypertensives (e.g., ACE inhibitors, ARBs, beta-blockers):** Reduced antihypertensive effect and increased risk of renal impairment.
* **Lithium:** Increased serum lithium levels and risk of toxicity. Monitor lithium levels.
* **Methotrexate:** Increased risk of methotrexate toxicity.
* **Selective Serotonin Reuptake Inhibitors (SSRIs):** Increased risk of gastrointestinal bleeding.
## Monitoring
* Monitor for signs and symptoms of gastrointestinal bleeding (e.g., melena, hematemesis).
* Monitor for signs and symptoms of renal toxicity (e.g., changes in urine output, elevated BUN/creatinine).
* Monitor for signs and symptoms of hepatic dysfunction (e.g., jaundice, elevated LFTs).
* Monitor blood pressure, especially when used concurrently with antihypertensives.
* In patients with chronic use, consider periodic renal and hepatic function tests.
## Clinical Pearls
* Mefenamic acid should be taken with food or milk to minimize gastrointestinal upset.
* Due to its potential for diarrhea, it is often not the first-line NSAID for chronic pain management.
* The onset of action for pain relief is typically within 1 hour.
* Duration of therapy should be limited to the shortest effective period.
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***Disclaimer:** This information is intended for healthcare professionals. Always consult the official prescribing information and relevant clinical guidelines for the most current and comprehensive details. Dosing and safety information can vary based on patient-specific factors and local protocols.*
