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# Mefenamic Acid
## Overview
Mefenamic acid is a nonsteroidal anti-inflammatory drug (NSAID) belonging to the fenamate class. It has analgesic and anti-inflammatory properties, primarily acting by inhibiting cyclooxygenase (COX) enzymes, thus reducing prostaglandin synthesis.
## Primary Indications
* Short-term relief of mild to moderate pain, including menstrual pain (dysmenorrhea), headache, dental pain, and muscle pain.
* Management of signs and symptoms of rheumatoid arthritis and osteoarthritis (though less commonly used for these chronic conditions compared to other NSAIDs).
## Adult Dosing
* **Pain:** 500 mg every 6 hours as needed. Dosing should not exceed 7 days for self-medication or 14 days under medical supervision.
* **Dysmenorrhea:** 500 mg initially, followed by 250 mg every 6 hours as needed.
* **Rheumatoid Arthritis/Osteoarthritis:** 500 mg three times daily. The maximum daily dose for adults is 1500 mg.
## Pediatric Dosing
Mefenamic acid is **not generally recommended for children under 12 years of age** due to lack of established dosing and safety data.
## Dose Adjustments
* **Renal Impairment:** Use with caution. Reduced doses may be necessary. Monitor renal function closely.
* **Hepatic Impairment:** Use with caution. Monitor liver function closely.
## Contraindications
* 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 (GI) bleeding or ulceration.
* Severe renal or hepatic impairment.
## Adverse Effects
* **Common:** Diarrhea (most common and can be severe), nausea, vomiting, abdominal pain, constipation, dizziness, rash.
* **Serious:** Gastrointestinal bleeding, ulceration, and perforation; cardiovascular thrombotic events (MI, stroke); renal failure; hepatic failure; hypersensitivity reactions; exacerbation of asthma; Stevens-Johnson syndrome, toxic epidermal necrolysis.
## Key Drug Interactions
* **Anticoagulants (e.g., warfarin):** Increased risk of bleeding.
* **Corticosteroids:** Increased risk of GI ulceration and bleeding.
* **SSRIs/SNRIs:** Increased risk of GI bleeding.
* **ACE inhibitors, ARBs, Diuretics:** Reduced antihypertensive effect and increased risk of renal impairment.
* **Lithium:** Increased lithium levels and toxicity.
* **Methotrexate:** Increased risk of methotrexate toxicity.
## Monitoring
* **GI symptoms:** Assess for signs of bleeding or ulceration.
* **Renal function:** Monitor BUN, creatinine, and urine output, especially in patients with pre-existing renal disease or those on concurrent nephrotoxic agents.
* **Hepatic function:** Monitor LFTs, especially with long-term use or in patients with hepatic impairment.
* **Blood pressure:** NSAIDs can elevate blood pressure.
* **Signs of hypersensitivity:** Monitor for rash, bronchospasm, or anaphylaxis.
## Clinical Pearls
* Mefenamic acid has a relatively short half-life, requiring frequent dosing.
* Diarrhea is a particularly common and potentially severe side effect, especially with higher doses or prolonged use. Patients should be advised to discontinue the drug and seek medical attention if severe diarrhea occurs.
* Consider co-administration with a proton pump inhibitor (PPI) or misoprostol for patients at high risk of GI complications.
* Due to the risk of serious adverse effects, mefenamic acid should be used at the lowest effective dose for the shortest duration necessary.
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*This information is intended for healthcare professionals and should not be used as a substitute for professional medical advice. Always consult the most current prescribing information and relevant clinical guidelines before making treatment decisions.*
