A 48-year-old woman with newly diagnosed rheumatoid arthritis (RA) and moderate disease activity (DAS28 5.2) presents for treatment initiation. She has no prior DMARD exposure. Which is the drug of choice for first-line monotherapy in this patient?

Explanation

## First-Line DMARD Monotherapy in RA **Key Point:** Methotrexate (MTX) is the gold standard and preferred first-line DMARD for all patients with newly diagnosed RA, regardless of disease activity, due to its efficacy, tolerability, and cost-effectiveness [cite:Harrison 21e Ch 313]. ### Why Methotrexate? 1. **Efficacy & Safety Profile** - Rapid onset of action (4–8 weeks) - Sustained remission rates in 30–40% of patients when used as monotherapy - Well-established safety monitoring protocols - Reversible toxicity with appropriate monitoring 2. **Mechanism** - Inhibits dihydrofolate reductase → reduced purine/pyrimidine synthesis - Anti-inflammatory effects via adenosine release - Synergistic with biologics (TNF inhibitors, IL-6 inhibitors) 3. **Dosing & Monitoring** - Starting dose: 7.5–10 mg once weekly (oral or parenteral) - Titrate to 15–25 mg/week based on response - Requires baseline CBC, LFTs, renal function; repeat every 8–12 weeks - Folic acid 5 mg daily (except on MTX day) to reduce toxicity **Clinical Pearl:** MTX is the backbone of combination DMARD therapy and is retained even when biologics are added, due to synergistic benefit and cost reduction. **High-Yield:** In NEET PG exams, MTX is the default first-line answer for early RA unless the stem specifies contraindications (pregnancy, renal failure, hepatic disease, or cytopenias). ### Comparison with Other DMARDs | Feature | Methotrexate | Leflunomide | Sulfasalazine | Biologics (TNFi) | |---------|--------------|-------------|---------------|------------------| | **Onset** | 4–8 weeks | 6–12 weeks | 6–12 weeks | 2–4 weeks | | **Monotherapy efficacy** | Excellent | Good | Moderate | Excellent | | **Cost** | Low | Moderate | Low | Very high | | **First-line role** | Yes (preferred) | Alternative | Alternative | Reserved for inadequate MTX response | | **Pregnancy** | Contraindicated | Contraindicated | Relative CI | Relative CI | | **Monitoring** | CBC, LFTs, Cr | LFTs, Cr | CBC, LFTs | TB screening, CBC | **Warning:** Do not confuse MTX with other immunosuppressants — it is NOT an immunosuppressant in the classical sense but rather a DMARD with anti-inflammatory properties.