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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. ## Primary Indications * Short-term management of mild to moderate pain, including pain associated with dysmenorrhea, headache, dental pain, and musculoskeletal pain. * Management of menorrhagia (heavy menstrual bleeding). ## Adult Dosing * **Pain:** 500 mg every 6 hours as needed. Do not exceed 1500 mg in the first 24 hours, and subsequent doses should not exceed 1250 mg per day. * **Menorrhagia:** 500 mg every 6 hours, starting at the onset of bleeding and associated pain, for a maximum of 5 days. ## Pediatric Dosing * Mefenamic acid is generally not recommended for use in children under 14 years of age for pain management due to lack of established efficacy and safety data. * For juvenile idiopathic arthritis, doses of 15-25 mg/kg/day divided into 3-4 doses have been used, but specific recommendations are often based on specialist guidance and local protocols. Maximum daily dose should not exceed 1000 mg. ## Dose Adjustments * **Renal Impairment:** Use with caution. Dose reduction may be necessary in severe renal impairment. Data is limited. * **Hepatic Impairment:** Use with caution. Dose reduction may be necessary in severe hepatic impairment. Data is limited. * **Elderly:** Elderly patients may be at increased risk of adverse effects; consider lower doses. ## Contraindications * Hypersensitivity to mefenamic acid, aspirin, or other NSAIDs. * History of bronchospasm, 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 (e.g., Crohn's disease, ulcerative colitis). * History of gastrointestinal bleeding or perforation related to previous NSAID use. * Active peptic ulceration or bleeding. * Severe heart failure, renal impairment, or hepatic impairment. * Pregnancy: Avoid use in the third trimester. Use in the first and second trimesters should be carefully considered and only if clearly needed. ## Adverse Effects * **Common:** Diarrhea, nausea, vomiting, abdominal pain, constipation, dizziness, headache, rash. * **Serious:** Gastrointestinal bleeding, ulceration, and perforation; cardiovascular thrombotic events (MI, stroke); renal papillary necrosis and other renal injury; hepatic dysfunction; hypersensitivity reactions (including anaphylaxis); bronchospasm; Stevens-Johnson syndrome/toxic epidermal necrolysis. ## Key Drug Interactions * **Anticoagulants (e.g., warfarin):** Increased risk of bleeding. Monitor INR closely. * **Corticosteroids:** Increased risk of gastrointestinal ulceration and bleeding. * **Selective Serotonin Reuptake Inhibitors (SSRIs) / Serotonin-Norepinephrine Reuptake Inhibitors (SNRIs):** Increased risk of gastrointestinal bleeding. * **Other NSAIDs (including aspirin):** Increased risk of gastrointestinal adverse effects, and potential for additive analgesic effects. * **ACE Inhibitors / Angiotensin II Receptor Blockers (ARBs):** Reduced antihypertensive efficacy and increased risk of renal impairment. * **Diuretics:** Reduced diuretic efficacy and increased risk of nephrotoxicity. * **Lithium:** Increased lithium levels and risk of toxicity. * **Methotrexate:** Increased methotrexate toxicity. ## Monitoring * **Baseline and periodic renal function tests.** * **Baseline and periodic liver function tests.** * **Signs and symptoms of gastrointestinal bleeding** (e.g., melena, hematemesis). * **Blood pressure.** * **For patients with cardiovascular risk factors, monitor for signs of cardiovascular events.** ## Clinical Pearls * Mefenamic acid should be taken with food or milk to minimize gastrointestinal upset. * Duration of use should be as short as possible to minimize risks. * It is a prescription-only medication and should not be used for self-treatment beyond recommended durations. * Discontinue use immediately if signs of serious adverse effects (e.g., GI bleeding, severe rash, renal dysfunction) occur. *** **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 relevant guidelines for complete details before making any treatment decisions.