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# Mefenamic Acid
## Overview
Mefenamic acid is a nonsteroidal anti-inflammatory drug (NSAID) belonging to the fenamate class. It is thought to exert its anti-inflammatory, analgesic, and antipyretic effects by inhibiting cyclooxygenase (COX) enzymes, thereby reducing prostaglandin synthesis.
## Primary Indications
* Mild to moderate pain, including menstrual pain (dysmenorrhea).
* Rheumatoid arthritis and osteoarthritis (less commonly used due to GI toxicity profile).
## 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.
* **Maximum daily dose:** 1500 mg. Treatment should generally not exceed 7 days.
## Pediatric Dosing
Mefenamic acid is not typically recommended for use in children under 14 years of age due to limited data and potential for adverse effects.
## Dose Adjustments
* **Renal Impairment:** Use with caution. Data on specific dose adjustments is limited, but reduced doses may be considered in severe impairment.
* **Hepatic Impairment:** Use with caution. Data on specific dose adjustments is limited, but reduced doses may be considered in severe impairment.
* **Elderly:** Consider lower doses and increased monitoring for GI bleeding, renal dysfunction, and cardiovascular events.
## Contraindications
* Known hypersensitivity to mefenamic acid, aspirin, or other NSAIDs.
* History of gastrointestinal bleeding or perforation related to previous NSAID use.
* Active peptic ulceration or a history of recurrent peptic ulceration.
* Severe heart failure.
* Third trimester of pregnancy.
## Adverse Effects
* **Common:** Diarrhea (often dose-limiting), nausea, vomiting, abdominal pain, constipation, dyspepsia, rash, dizziness, headache.
* **Serious:** Gastrointestinal bleeding, perforation, ulceration; renal impairment; hepatic dysfunction; Stevens-Johnson syndrome; toxic epidermal necrolysis; aseptic meningitis; cardiovascular thrombotic events; exacerbation of asthma; hypersensitivity reactions.
## Key Drug Interactions
* **Anticoagulants (e.g., warfarin):** Increased risk of bleeding.
* **Corticosteroids:** Increased risk of GI ulceration and bleeding.
* **Other NSAIDs (including aspirin):** Increased risk of GI toxicity and reduced cardioprotective effects of low-dose aspirin.
* **Diuretics and Antihypertensives (e.g., ACE inhibitors, ARBs, beta-blockers):** Reduced antihypertensive efficacy, increased risk of renal impairment.
* **Lithium:** Increased serum lithium levels and risk of toxicity.
* **Methotrexate:** Increased methotrexate levels and risk of toxicity.
* **Selective Serotonin Reuptake Inhibitors (SSRIs) / Serotonin-Norepinephrine Reuptake Inhibitors (SNRIs):** Increased risk of GI bleeding.
## Monitoring
* Signs and symptoms of gastrointestinal bleeding (e.g., melena, hematemesis).
* Renal function (BUN, creatinine).
* Liver function tests (ALT, AST).
* Blood pressure.
* Signs of fluid retention or edema.
## Clinical Pearls
* Mefenamic acid has a relatively short half-life, necessitating frequent dosing for sustained pain relief.
* Diarrhea is a common and often dose-limiting side effect; discontinue if severe diarrhea occurs.
* Should be used at the lowest effective dose for the shortest duration necessary to minimize risks.
* Avoid concurrent use with other NSAIDs.
* Advise patients to report any signs of bleeding or unusual bruising.
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**Disclaimer:** This information is intended for healthcare professionals and is not a substitute for professional medical advice. Always consult the most current prescribing information and your institution's protocols for definitive guidance.
