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# Mefenamic Acid ## Overview Mefenamic acid is a nonsteroidal anti-inflammatory drug (NSAID) belonging to the fenamate class. It exhibits analgesic, anti-inflammatory, and antipyretic properties through the inhibition of cyclooxygenase (COX) enzymes, thereby reducing prostaglandin synthesis. ## Primary Indications * Short-term management of mild to moderate pain, particularly: * Menstrual pain (dysmenorrhea) * Post-operative pain * Dental pain * Management of osteoarthritis and rheumatoid arthritis (though generally not first-line). ## Adult Dosing * **Pain:** 500 mg every 8 hours as needed. Do not exceed 1500 mg daily for short-term use. * **Dysmenorrhea:** 500 mg initially, followed by 250 mg every 6 hours as needed. Treatment typically starts at the onset of pain or bleeding and continues for no more than 6 days per month. * **Arthritis:** Dosing varies; generally not recommended for chronic use due to risk-benefit profile compared to other NSAIDs. ## Pediatric Dosing * **Mefenamic acid is generally not recommended for children under 14 years of age.** Safety and efficacy in this population have not been established. ## Dose Adjustments * **Renal Impairment:** Use with caution. Dose reduction may be necessary in severe renal impairment, though specific guidelines are lacking. Monitor renal function closely. * **Hepatic Impairment:** Use with caution. No specific dose adjustments are established, but consider reduced doses and close monitoring for signs of liver dysfunction. ## Contraindications * Known hypersensitivity to mefenamic acid, aspirin, or other NSAIDs. * History of bronchospasm, urticaria, or allergic-type reactions after taking aspirin or other NSAIDs. * Peri-operative pain in the setting of coronary artery bypass graft (CABG) surgery. * Active gastrointestinal (GI) bleeding or history of recurrent GI ulceration/bleeding. * Severe heart failure, severe renal impairment, or severe hepatic impairment. * Third trimester of pregnancy. ## Adverse Effects * **Common:** Nausea, vomiting, diarrhea, abdominal pain, constipation, dyspepsia, dizziness, rash. * **Serious:** * **GI:** Ulceration, bleeding, perforation. * **Cardiovascular:** Increased risk of myocardial infarction and stroke. * **Renal:** Acute kidney injury, interstitial nephritis. * **Hepatic:** Hepatotoxicity. * **Hematologic:** Anemia, leukopenia. * **Hypersensitivity:** Anaphylaxis, Stevens-Johnson syndrome, toxic epidermal necrolysis. ## Key Drug Interactions * **Anticoagulants (e.g., warfarin):** Increased risk of bleeding. * **Aspirin:** May decrease the cardioprotective effect of low-dose aspirin; concurrent use is generally not recommended due to increased GI risk. * **Corticosteroids:** Increased risk of GI ulceration and bleeding. * **Diuretics and Antihypertensives:** May reduce their efficacy and increase risk of renal toxicity. * **Lithium:** Increased serum lithium levels and risk of toxicity. * **Methotrexate:** Increased risk of methotrexate toxicity. * **Other NSAIDs:** Increased risk of adverse effects, especially GI bleeding. ## Monitoring * **Gastrointestinal:** Monitor for signs and symptoms of GI bleeding and ulceration (e.g., black, tarry stools, hematemesis, abdominal pain). * **Renal Function:** Monitor serum creatinine and BUN, especially in patients with pre-existing renal disease or those on concomitant nephrotoxic agents. * **Hepatic Function:** Monitor liver enzymes, especially in patients with known liver disease. * **Cardiovascular Risk:** Assess and manage cardiovascular risk factors. ## Clinical Pearls * Mefenamic acid is generally intended for **short-term use** due to the risk of serious adverse effects, particularly GI complications. * It should be taken with food or milk to minimize GI upset. * Its onset of action for pain relief is typically within 1-2 hours. * Due to potential for dizziness, caution patients when driving or operating machinery. * Consider individual patient risk factors for GI, renal, and cardiovascular adverse events before initiating therapy. *** *This information is intended for healthcare professionals and should not substitute for professional medical advice. Always consult the most current prescribing information and clinical guidelines before making any treatment decisions.*