Mefenamic Acid

# Mefenamic acid ## Overview - **Classification**: Non-Steroidal Anti-Inflammatory Drug (NSAID) - Anthranilic acid derivative. - **Mechanism**: Inhibits cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis responsible for inflammation, pain, and fever. ## Primary Indications 1. **Mild to Moderate Pain**: Short-term management. 2. **Primary Dysmenorrhea**: Relief of menstrual cramps. 3. **Menorrhagia**: Reduction of heavy menstrual bleeding. ## Adult Dosing ### Standard Dosing **Mild to Moderate Pain / Primary Dysmenorrhea** - **Dose**: Initial **500 mg** - **Frequency**: Then **250 mg** every 6 hours - **Route**: Oral - **Duration**: Max **7 days** for pain; Max **2-3 days** for dysmenorrhea **Menorrhagia** - **Dose**: **500 mg** - **Frequency**: Three times daily (TID) - **Route**: Oral - **Duration**: During heavy bleeding, max **7 days** ### Dose Adjustments - **Renal Impairment**: Avoid use if **CrCl < 30 mL/min**. Use with caution in mild-moderate impairment. - **Hepatic Impairment**: Use with caution. Avoid in severe hepatic impairment. - **Elderly Patients**: Increased risk of GI, renal, and CV adverse effects. Use lowest effective dose for shortest duration. ## Pediatric Dosing *Mefenamic acid is generally not recommended for routine use in children due to safety concerns and availability of safer alternatives, especially in younger age groups.* ### Neonates (0-28 days) - **Dose**: **Not recommended.** - **Special Notes**: High risk of renal, GI, and CNS adverse effects. ### Infants (1-12 months) - **Dose**: **Not recommended.** - **Special Notes**: Lack of safety and efficacy data. ### Children (1-12 years) - **Dose**: **Generally not recommended** due to safety concerns (e.g., convulsions). - **Special Notes**: If used for very specific indications (e.g., juvenile idiopathic arthritis, though now largely historical), **20-25 mg/kg/day** in divided doses. This is **rarely used** and **discouraged.** ### Adolescents (13-18 years) - **Dose**: May follow **adult dosing** for specified indications. - **Maximum**: **1250 mg/day**. Max **7 days** duration. - **Special Notes**: Ensure patient is >12 years old. ## Safety Information ### Contraindications - **Absolute**: Hypersensitivity to mefenamic acid, aspirin, or other NSAIDs. - **Absolute**: Active peptic ulcer disease or history of recurrent GI bleeding/ulceration. - **Absolute**: Severe renal or hepatic impairment. - **Absolute**: Inflammatory bowel disease (Crohn's, Ulcerative Colitis). - **Absolute**: History of aspirin-induced asthma, urticaria, or allergic-type reactions. - **Absolute**: Peri-operative pain in the setting of Coronary Artery Bypass Graft (CABG) surgery. - **Absolute**: Third trimester of pregnancy. ### Common Adverse Effects - **Common (1-10%)**: Diarrhea, abdominal pain, nausea, vomiting, dyspepsia, headache, dizziness. - **Serious but Rare**: GI bleeding/ulceration/perforation, acute kidney injury, severe allergic reactions (anaphylaxis, SJS), thrombotic events (MI, stroke), agranulocytosis, hemolytic anemia. ### Key Drug Interactions - **Anticoagulants (e.g., Warfarin)**: Increased bleeding risk. Monitor INR closely. - **Lithium**: Increased lithium levels, leading to toxicity. Monitor lithium levels. - **Diuretics (e.g., Furosemide, Thiazides)**: Reduced diuretic and antihypertensive effect. Monitor BP, renal function. - **ACE Inhibitors/ARBs**: Increased risk of renal impairment, hyperkalemia. Monitor renal function, K+. - **Methotrexate**: Increased methotrexate toxicity. Avoid or monitor closely. - **SSRIs**: Increased risk of GI bleeding. Use caution. - **Corticosteroids**: Increased risk of GI ulceration/bleeding. Consider PPI co-prescription. ## Monitoring & Follow-up - **Before Treatment**: Assess GI risk factors, renal/hepatic function, baseline blood pressure. - **During Treatment**: Monitor for signs of GI bleeding (e.g., black stools, coffee-ground emesis), rash, edema, changes in urine output. - **Clinical Signs**: Watch for unexplained weight gain, shortness of breath, or jaundice. ## Clinical Pearls - 💡 **Tip 1**: Take with food, milk, or antacids to minimize GI upset. - 💡 **Tip 2**: Not for long-term use; treatment duration generally limited to **7 days** due to increased risk of serious adverse effects. - 💡 **Tip 3**: May cause diarrhea, which can be severe. Discontinue if persistent diarrhea occurs. - 💡 **Tip 4**: Mefenamic acid can cause a false-positive reaction for urinary bilirubin. > **⚠️ Important**: This information is for educational purposes only. Always consult current prescribing information, local guidelines, and clinical judgment before prescribing.