Mefenemic Acid

# Mefenemic acid ## Overview - **Classification**: Non-Steroidal Anti-Inflammatory Drug (NSAID), Fenamate class - **Mechanism**: Inhibits cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis. This leads to anti-inflammatory, analgesic, and antipyretic effects. ## Primary Indications 1. **Mild-to-moderate pain**: Acute pain, e.g., musculoskeletal pain. 2. **Primary Dysmenorrhea**: Menstrual cramps. 3. **Menorrhagia**: Heavy menstrual bleeding (off-label or specific regions). ## Adult Dosing ### Standard Dosing **Acute Pain** - **Dose**: **500 mg** - **Frequency**: Initial dose, then **250 mg** every 6 hours PRN - **Route**: Oral - **Duration**: Max **7 days** due to increased risk of adverse effects **Primary Dysmenorrhea** - **Dose**: **500 mg** - **Frequency**: Initial dose, then **250 mg** every 6 hours PRN - **Route**: Oral - **Duration**: Max **2-3 days** (start with onset of menses/symptoms) ### Dose Adjustments - **Renal Impairment**: **Contraindicated** in severe renal impairment (CrCl < 30 mL/min). Use with caution in mild-moderate. - **Hepatic Impairment**: **Contraindicated** in severe hepatic impairment. Use with caution in mild-moderate. - **Elderly Patients**: Use lowest effective dose for shortest duration. Increased risk of GI/renal adverse effects. ## Pediatric Dosing **Note**: Mefenamic acid is generally not recommended for children under 14 years due to potential for seizures and other serious adverse effects. ### Neonates (0-28 days) - **Contraindicated**: Due to high risk of renal and CNS adverse effects. - **Special Notes**: NSAIDs generally avoided in this age group. ### Infants (1-12 months) - **Not Recommended**: Safety and efficacy not established. Risk of seizure, GI, renal toxicity. ### Children (1-12 years) - **Not Recommended**: Safety and efficacy not established. **Contraindicated for dysmenorrhea under 14 years.** Limited use for pain in some regions, but generally discouraged. ### Adolescents (13-18 years) - **Dysmenorrhea (≥14 years)**: Treat as adult dosing. - **Dose**: **500 mg** initial, then **250 mg** every 6 hours PRN. - **Maximum**: **1000 mg/day**. Max duration **2-3 days**. - **Acute Pain (≥14 years)**: Treat as adult dosing. - **Dose**: **500 mg** initial, then **250 mg** every 6 hours PRN. - **Maximum**: **1000 mg/day**. Max duration **7 days**. ## Safety Information ### Contraindications - **Absolute**: Hypersensitivity to mefenamic acid or other NSAIDs/aspirin (e.g., aspirin-induced asthma, urticaria, allergic-type reactions). - **Absolute**: Active gastrointestinal (GI) bleeding or peptic ulcer disease. - **Absolute**: Severe renal impairment (CrCl < 30 mL/min) or severe hepatic impairment. - **Absolute**: Peri-operative pain in the setting of coronary artery bypass graft (CABG) surgery. - **Absolute**: Severe uncontrolled heart failure (NYHA Class III/IV). - **Absolute**: Children **under 14 years** for dysmenorrhea (and generally for other indications). - **Absolute**: Inflammatory bowel disease (e.g., Crohn's disease, ulcerative colitis). ### Common Adverse Effects - **Very Common (>10%)**: Diarrhea, nausea, abdominal pain. - **Common (1-10%)**: Vomiting, dyspepsia, constipation, dizziness, headache, tinnitus, rash, edema. - **Serious but Rare**: GI bleeding/ulceration, acute kidney injury, severe hepatic dysfunction, aplastic anemia, hemolytic anemia, Stevens-Johnson syndrome, myocardial infarction, stroke, **seizures** (especially in pediatric patients). ### Key Drug Interactions - **Anticoagulants (e.g., Warfarin)**: Increased risk of bleeding. **Monitor INR closely.** - **Lithium**: Increased lithium plasma levels and toxicity. **Monitor lithium levels.** - **Methotrexate**: Increased methotrexate plasma levels and toxicity. **Avoid concurrent use.** - **Diuretics (e.g., Furosemide), ACE Inhibitors, ARBs**: Decreased antihypertensive effect, increased risk of renal impairment. **Monitor BP and renal function.** - **SSRIs/SNRIs**: Increased risk of GI bleeding. - **Cyclosporine/Tacrolimus**: Increased risk of nephrotoxicity. - **Corticosteroids**: Increased risk of GI ulceration and bleeding. ## Monitoring & Follow-up - **Before Treatment**: Assess renal and hepatic function, obtain baseline CBC (if prolonged use anticipated). - **During Treatment**: Monitor for signs of GI bleeding (black stools), edema, blood pressure. - **Clinical Signs**: Watch for unexplained weight gain, rash, persistent diarrhea (may require discontinuation), jaundice, dark urine. ## Clinical Pearls - 💡 **Short-term use**: Limit duration to **7 days** for pain and **2-3 days** for dysmenorrhea to minimize adverse effects. - 💡 **Administration**: Take with food, milk, or antacids to reduce GI upset. - 💡 **Diarrhea**: Mefenamic acid is particularly associated with diarrhea; discontinue if severe or persistent. - 💡 **Seizure Risk**: Due to the unique risk of seizures, especially in children, its use is more restricted than other NSAIDs. - 💡 **Patient Counseling**: Advise patients to report any signs of GI bleeding, unusual bruising, rash, or changes in urination. > **⚠️ Important**: This information is for educational purposes only. Always consult current prescribing information, local guidelines, and clinical judgment before prescribing.