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# Mefenamic Acid
## Overview
Mefenamic acid is a nonsteroidal anti-inflammatory drug (NSAID) belonging to the fenamate class. It is a non-selective cyclooxygenase (COX) inhibitor, meaning it inhibits both COX-1 and COX-2 enzymes, which are involved in the synthesis of prostaglandins.
## Primary Indications
* Short-term management of mild to moderate pain, including pain associated with menstrual cramps (dysmenorrhea).
* Relief of inflammatory and analgesic symptoms of rheumatoid arthritis and osteoarthritis.
## Adult Dosing
* **Pain:** 500 mg every 6 hours as needed. Do not exceed 7 days of treatment for pain.
* **Dysmenorrhea:** 500 mg every 6 hours starting at the onset of pain or bleeding, whichever comes first, for the duration of symptoms, not to exceed 7 days.
* **Rheumatoid Arthritis/Osteoarthritis:** 500 mg every 6 hours. Some patients may respond to 250 mg every 6 hours. The maximum daily dose is typically 1500 mg, but may be increased to 2000 mg per day in some cases, under medical supervision, for short-term use.
## Pediatric Dosing
* Mefenamic acid is generally not recommended for use in children under 14 years of age due to limited efficacy and safety data. Some sources suggest it may be used in children over 6 months of age for fever and pain, but specific dosing is highly variable and requires careful clinical judgment and is often based on weight (e.g., 6.5 mg/kg/dose every 6-8 hours, not to exceed 4 doses/day). **Local protocols and specific product labeling should be consulted.**
## Dose Adjustments
* **Renal Impairment:** Use with caution. May require dose reduction; however, specific guidelines are lacking. Monitor for signs of renal toxicity.
* **Hepatic Impairment:** Use with caution. May require dose reduction; however, specific guidelines are lacking. Monitor liver function.
## Contraindications
* Hypersensitivity to mefenamic acid, aspirin, 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.
* Inflammatory bowel disease.
* Severe renal or hepatic impairment.
* Advanced heart failure.
## Adverse Effects
* **Gastrointestinal:** Nausea, vomiting, diarrhea, abdominal pain, dyspepsia, constipation. Most common and serious: GI bleeding, ulceration, perforation.
* **Renal:** Acute kidney injury, interstitial nephritis, papillary necrosis.
* **Cardiovascular:** Increased risk of thrombotic events (MI, stroke), edema, hypertension.
* **Hepatic:** Elevated liver enzymes, hepatic failure.
* **Hematologic:** Anemia, thrombocytopenia, leukopenia.
* **Dermatologic:** Rash, pruritus, Stevens-Johnson syndrome, toxic epidermal necrolysis.
* **Other:** Drowsiness, dizziness, headache.
## Key Drug Interactions
* **Anticoagulants (e.g., warfarin):** Increased risk of bleeding.
* **Corticosteroids:** Increased risk of GI ulceration and bleeding.
* **Diuretics and antihypertensives:** May reduce their efficacy and increase risk of nephrotoxicity.
* **Lithium:** Increased lithium levels.
* **Methotrexate:** Increased methotrexate toxicity.
* **Other NSAIDs or salicylates:** Increased risk of GI adverse effects and no demonstrated synergistic benefit.
## Monitoring
* Monitor for signs and symptoms of GI bleeding (e.g., melena, hematemesis).
* Monitor renal function (BUN, creatinine) especially in patients with pre-existing renal disease or those at risk.
* Monitor liver function tests (ALT, AST) especially with prolonged use or in patients with hepatic impairment.
* Monitor blood pressure.
* Assess for signs of hypersensitivity reactions.
## Clinical Pearls
* Mefenamic acid should be taken with food or milk to minimize gastrointestinal upset.
* It is intended for short-term use only. Long-term use is associated with increased risks.
* Considered a potent analgesic but is also associated with a higher incidence of GI side effects compared to some other NSAIDs.
* Use the lowest effective dose for the shortest duration necessary to reduce the risk of adverse events.
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**Disclaimer:** This information is for educational purposes only and does not substitute for professional medical advice. Always consult with a qualified healthcare provider and refer to the most current prescribing information or official drug compendium for complete details before making any treatment decisions.
