A 40-year-old man presents with new-onset symmetric pain and swelling of the metacarpophalangeal and proximal interphalangeal joints bilaterally lasting more than 8 weeks. Morning stiffness lasts over an hour. Physical examination shows synovitis in multiple joints. Rheumatoid factor and anti-cyclic citrullinated peptide antibodies are positive. What is the most appropriate initial disease-modifying therapy?