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# Mefenamic acid
## Overview
Nonsteroidal anti-inflammatory drug (NSAID) of the fenamate class. Inhibits COX-1 and COX-2, reducing prostaglandin synthesis. Used for mild-to-moderate pain, particularly dysmenorrhea and musculoskeletal pain.
## Primary Indications
- Primary dysmenorrhea
- Mild-to-moderate acute pain (e.g., headache, dental pain, musculoskeletal pain)
- Juvenile rheumatoid arthritis (second-line in selected pediatric patients)
## Adult Dosing
- **Initial**: 500 mg orally once (loading)
- **Maintenance**: 250 mg orally every 6 hours as needed
- **Maximum daily dose**: 1,000 mg (1 g) per day
- Duration should be limited to 7 days for acute pain; for dysmenorrhea, start with onset of menses and continue for 2–3 days.
## Pediatric Dosing
- **Children ≥14 years** (or body weight >50 kg): Same as adult dosing.
- **Children <14 years**: Not routinely recommended; use only under specialist guidance.
- **Juvenile rheumatoid arthritis**: 5–7.5 mg/kg/dose orally every 6–8 hours; maximum 25 mg/kg/day.
- Dosing may vary by local protocol; consult pediatric reference if used.
## Dose Adjustments
- **Renal impairment**: Avoid in moderate-to-severe renal impairment (CrCl <30 mL/min). Use with caution in mild impairment; reduce dose or extend interval.
- **Hepatic impairment**: Avoid in severe liver disease. Use with caution in mild–moderate impairment; consider dose reduction.
- **Elderly**: Use lowest effective dose; monitor closely for GI bleeding and renal function.
## Contraindications
- Hypersensitivity to mefenamic acid or any NSAID (including aspirin-induced asthma)
- Active peptic ulcer disease or GI bleeding
- Severe renal or hepatic impairment
- History of cardiovascular disease (e.g., recent MI, stroke, coronary bypass surgery)
- Third trimester of pregnancy (risk of premature ductus arteriosus closure)
- Bleeding disorders or concurrent anticoagulation (relative, use with extreme caution)
## Adverse Effects
- **Common**: Nausea, dyspepsia, diarrhea (including bloody diarrhea), headache, dizziness
- **Serious**: GI ulceration/bleeding, renal impairment, hypertension, acute interstitial nephritis, hepatic dysfunction, hemolytic anemia (rare), thrombocytopenia, anaphylaxis
- **Note**: Risk of CV thrombotic events with long-term use.
## Key Drug Interactions
- **Anticoagulants (warfarin, DOACs)**: Increased bleeding risk
- **Aspirin/other NSAIDs**: Additive GI toxicity
- **Lithium, methotrexate, digoxin**: Increased serum levels due to reduced renal clearance
- **ACE inhibitors, ARBs, diuretics**: Reduced antihypertensive effect; increased risk of renal impairment
- **Antiplatelet agents (clopidogrel)**: Enhanced bleeding risk
## Monitoring
- **Before & periodically**: Renal function (Cr, BUN), liver function (ALT/AST), CBC (especially if therapy >1 week)
- **Symptoms**: Monitor for GI bleeding (melena, hematemesis), edema, worsening pain, stool color changes
- **Duration**: Limit use to shortest effective course; avoid chronic use if possible
## Clinical Pearls
- **Food**: Take with food or milk to reduce GI upset.
- **Dysmenorrhea**: Start 500 mg at onset of menses, then 250 mg q6h PRN for 1–2 days.
- **Avoid in aspirin/NSAID triad** (asthma, nasal polyps, aspirin intolerance).
- **Not first-line** NSAID in most pain guidelines due to higher diarrhea risk; reserve for short-term use.
- **Do not exceed 1 g/day**; doses >2.5 g/day may cause seizures or rhabdomyolysis.
- **Pregnancy**: Contraindicated in third trimester; avoid in first and second unless clearly needed.
**Educational Disclaimer**: This information is for educational purposes only and does not substitute for professional clinical judgment. Always verify dosing with local drug monographs and individual patient factors.
