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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. Its mechanism of action involves the inhibition of cyclooxygenase (COX) enzymes, thereby reducing prostaglandin synthesis. ## Primary Indications * **Pain:** Management of mild to moderate pain, including menstrual pain (dysmenorrhea), headache, and dental pain. * **Inflammation:** Relief of inflammation associated with musculoskeletal conditions. ## Adult Dosing * **Pain and Dysmenorrhea:** * **Initial dose:** 500 mg every 8 hours as needed. * **Maximum duration:** Typically recommended for short-term use, not exceeding 7 days. * **Maximum daily dose:** 1500 mg. * **Note:** Some guidelines suggest a maximum of 1000 mg every 8 hours for severe pain, but this should be guided by patient response and tolerability. Always adhere to local protocols. ## Pediatric Dosing Mefenamic acid is generally not recommended for use in children under 14 years of age due to a lack of established efficacy and safety data, particularly concerning potential renal toxicity. ## Dose Adjustments * **Renal Impairment:** Use with caution. Dose reduction may be necessary in patients with severe renal impairment. Monitor renal function closely. * **Hepatic Impairment:** Use with caution. Dose reduction may be necessary in patients with severe hepatic impairment. Monitor hepatic function closely. * **Elderly:** Elderly patients are at increased risk of adverse effects, particularly gastrointestinal bleeding, renal impairment, and cardiovascular events. Lower doses and closer monitoring are recommended. ## Contraindications * 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 history of recurrent gastrointestinal ulceration or bleeding. * Severe renal impairment. * Severe hepatic impairment. * Severe heart failure. * Third trimester of pregnancy. ## Adverse Effects * **Gastrointestinal:** Dyspepsia, nausea, vomiting, abdominal pain, diarrhea, constipation, flatulence, peptic ulceration, gastrointestinal bleeding, perforation. * **Central Nervous System:** Dizziness, drowsiness, headache. * **Renal:** Renal insufficiency, acute kidney injury, interstitial nephritis, papillary necrosis (especially with prolonged use). * **Hematologic:** Anemia, leukopenia, thrombocytopenia. * **Dermatologic:** Rash, pruritus, Stevens-Johnson syndrome, toxic epidermal necrolysis. * **Cardiovascular:** Increased risk of serious cardiovascular thrombotic events, myocardial infarction, stroke, hypertension, edema. * **Other:** Bronchospasm (especially in aspirin-sensitive asthmatics), tinnitus, photosensitivity. ## Key Drug Interactions * **Anticoagulants (e.g., warfarin):** Increased risk of bleeding. * **Corticosteroids:** Increased risk of gastrointestinal ulceration and bleeding. * **Selective Serotonin Reuptake Inhibitors (SSRIs) and Serotonin-Norepinephrine Reuptake Inhibitors (SNRIs):** Increased risk of gastrointestinal bleeding. * **Other NSAIDs (including aspirin):** Increased risk of gastrointestinal adverse effects and potential for reduced efficacy of low-dose aspirin for cardioprotection. * **Diuretics and Antihypertensives:** May reduce their efficacy and increase the risk of renal impairment. * **Lithium:** NSAIDs can increase serum lithium levels and potentiate lithium toxicity. * **Methotrexate:** May increase methotrexate toxicity. ## Monitoring * **Gastrointestinal:** Monitor for signs and symptoms of bleeding (e.g., melena, hematemesis) and ulceration. Consider concomitant gastroprotective therapy (e.g., PPI) in high-risk patients. * **Renal Function:** Baseline and periodic monitoring of serum creatinine and BUN, especially in patients with pre-existing renal disease, dehydration, or those taking concomitant nephrotoxic agents. * **Hepatic Function:** Baseline and periodic monitoring of liver function tests, especially in patients with hepatic impairment. * **Hematologic:** Monitor complete blood count (CBC) for signs of anemia or other hematologic abnormalities. * **Blood Pressure:** Monitor blood pressure, particularly in patients with hypertension. * **Electrolytes:** Monitor electrolytes, especially in patients with renal impairment or those on diuretics. ## Clinical Pearls * Mefenamic acid has a relatively short half-life and is typically dosed every 8 hours. * It is generally recommended for short-term use only due to increased risk of adverse effects with prolonged administration. * Administer with food or milk to minimize gastrointestinal upset. * Be aware of the increased risk of cardiovascular thrombotic events, myocardial infarction, and stroke associated with NSAID use. * Avoid in patients with known hypersensitivity to aspirin or other NSAIDs. * Use cautiously in patients with pre-existing cardiovascular disease, renal impairment, hepatic impairment, or a history of gastrointestinal bleeding. *** **Disclaimer:** This information is intended for clinical use and is not a substitute for professional medical advice. Always consult the most current prescribing information and relevant clinical guidelines before making any treatment decisions. Verify all doses and safety information with the official drug product labeling.