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# Mefenamic Acid
## Overview
Mefenamic acid is a nonsteroidal anti-inflammatory drug (NSAID) belonging to the fenamate class. It inhibits cyclooxygenase (COX) enzymes, reducing prostaglandin synthesis.
## Primary Indications
* Short-term management of mild to moderate pain, including menstrual pain (dysmenorrhea).
* Management of rheumatoid arthritis and osteoarthritis (less commonly used due to GI risks).
## Adult Dosing
* **Pain:** 500 mg every 4 to 6 hours as needed. Do not exceed 1500 mg in any 24-hour period for the first 2 days of treatment, and then not more than 1000 mg per day thereafter.
* **Dysmenorrhea:** 500 mg initially, followed by 250 mg every 6 hours as needed. Treatment should begin at the onset of pain and bleeding and continue for the duration of dysmenorrhea.
* **Rheumatoid Arthritis/Osteoarthritis:** Typically 1500 mg daily in divided doses. Maximum daily dose is generally 1000 mg.
## Pediatric Dosing
* Mefenamic acid is generally not recommended for children under 14 years of age due to lack of established dosing and safety data.
## Dose Adjustments
* **Renal Impairment:** Use with caution. No specific dose adjustments are established, but reduced doses may be considered in severe impairment.
* **Hepatic Impairment:** Use with caution. No specific dose adjustments are established, but reduced doses may be considered in severe impairment.
* **Elderly:** Use with caution, higher risk of GI bleeding, renal dysfunction, and cardiovascular events. Lower doses may be considered.
## Contraindications
* Known hypersensitivity to mefenamic acid or other NSAIDs.
* History of asthma, urticaria, or allergic-type reactions after aspirin or other NSAIDs.
* Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery.
* Active gastrointestinal bleeding or ulceration.
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal pain, constipation, dyspepsia, headache, dizziness, rash.
* **Serious:** Gastrointestinal bleeding, perforation, ulceration; renal failure; hepatic failure; cardiovascular thrombotic events (MI, stroke); exacerbation of asthma; Stevens-Johnson syndrome, toxic epidermal necrolysis; hematologic effects (anemia, leukopenia).
## Key Drug Interactions
* **Anticoagulants (e.g., warfarin):** Increased risk of bleeding. Monitor INR closely.
* **Corticosteroids:** Increased risk of GI ulceration and bleeding.
* **SSRIs and SNRIs:** Increased risk of GI bleeding.
* **Diuretics, ACE Inhibitors, ARBs:** Reduced antihypertensive effect and increased risk of renal impairment.
* **Lithium:** Increased lithium levels and toxicity.
* **Methotrexate:** Increased methotrexate toxicity.
## Monitoring
* Signs and symptoms of GI bleeding (melena, hematemesis, abdominal pain).
* Renal function (BUN, creatinine).
* Liver function tests (ALT, AST).
* Blood pressure.
* For patients with chronic use, consider periodic CBC.
## Clinical Pearls
* Short-term use is preferred to minimize GI and cardiovascular risks.
* Administer with food or milk to reduce gastrointestinal upset.
* Avoid concurrent use with other NSAIDs.
* May mask signs of infection.
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**Disclaimer:** This information is intended for healthcare professionals. It is essential to consult the most current prescribing information and relevant clinical guidelines for definitive patient management. Dosing may vary based on specific patient factors and local protocols.
