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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 relief of mild to moderate pain, including menstrual pain (dysmenorrhea). * Relief of pain associated with osteoarthritis and rheumatoid arthritis. ## Adult Dosing * **Pain:** 500 mg every 6 hours as needed. Do not exceed 7 days of treatment. * **Dysmenorrhea:** 500 mg every 6 hours starting with the onset of pain or bleeding, whichever occurs first, and continuing for the duration of the symptoms, typically no longer than 7 days. * **Arthritis:** 750 mg every 6 hours. For longer-term use, consider lower doses. The maximum daily dose should not exceed 1500 mg. ## Pediatric Dosing Mefenamic acid is generally not recommended for use in children under 14 years of age for pain relief due to limited safety and efficacy data. Specific pediatric dosing for other indications is not well-established. ## Dose Adjustments * **Renal Impairment:** Use with caution. Dose reduction may be necessary in severe renal impairment. Specific guidance is lacking. * **Hepatic Impairment:** Use with caution. Dose reduction may be necessary in severe hepatic impairment. Specific guidance is lacking. * **Elderly:** Elderly patients may be at increased risk of adverse effects, particularly gastrointestinal bleeding, renal events, and cardiovascular thrombotic events. Consider lower doses. ## Contraindications * Known hypersensitivity to mefenamic acid or other NSAIDs. * History of bronchospasm, asthma, rhinitis, or urticaria following aspirin or other NSAIDs. * Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery. * Active gastrointestinal bleeding or history of recurrent gastrointestinal perforation, ulceration, or bleeding. * Severe heart failure. * Severe renal impairment. * Severe hepatic impairment. * Third trimester of pregnancy. ## Adverse Effects **Common:** * Gastrointestinal: Diarrhea (most common), nausea, vomiting, abdominal pain, dyspepsia, constipation, flatulence. * Central Nervous System: Dizziness, headache, drowsiness. **Serious:** * Cardiovascular: Increased risk of myocardial infarction, stroke, hypertension, and heart failure. * Gastrointestinal: Ulceration, perforation, bleeding (potentially fatal), exacerbation of inflammatory bowel disease. * Renal: Renal papillary necrosis and other renal injury, especially with prolonged use; interstitial nephritis, nephrotic syndrome, renal failure. * Hepatic: Elevated liver enzymes, jaundice, hepatitis, liver failure. * Hematologic: Anemia, leukopenia, thrombocytopenia, eosinophilia. * Hypersensitivity: Anaphylaxis, angioedema, rash, Stevens-Johnson syndrome, toxic epidermal necrolysis. * Respiratory: Bronchospasm, asthma exacerbation. ## Key Drug Interactions * **Anticoagulants (e.g., warfarin):** Increased risk of bleeding. * **Corticosteroids:** Increased risk of gastrointestinal bleeding. * **Selective Serotonin Reuptake Inhibitors (SSRIs):** Increased risk of gastrointestinal bleeding. * **Lithium:** Increased serum lithium levels and risk of toxicity. * **Methotrexate:** Increased risk of methotrexate toxicity. * **Diuretics, ACE inhibitors, Angiotensin II Receptor Blockers (ARBs):** Decreased antihypertensive efficacy and increased risk of renal impairment. * **Other NSAIDs:** Increased risk of gastrointestinal toxicity and additive pharmacologic effects. ## Monitoring * **For Short-Term Use:** Monitor for signs and symptoms of gastrointestinal bleeding (e.g., melena, hematemesis) and hypersensitivity reactions. * **For Longer-Term Use:** Monitor renal function (BUN, creatinine), liver function (AST, ALT), complete blood count (CBC), and blood pressure. Assess for signs of fluid retention and edema. ## Clinical Pearls * Mefenamic acid is generally intended for short-term use due to the risk of gastrointestinal and renal adverse effects. * Advise patients to take with food or milk to minimize gastrointestinal upset. * Due to the risk of diarrhea, which can be severe and prolonged, patients should be counseled to discontinue the medication and seek medical attention if severe or persistent diarrhea occurs. * Avoid concomitant use with other NSAIDs, including aspirin, unless specifically indicated and managed. *** **Disclaimer:** This information is intended for clinical use by healthcare professionals. Always verify current prescribing information and consult with appropriate resources before making clinical decisions. Dosages and recommendations may vary based on patient-specific factors and local protocols.