Step 1: In rheumatoid arthritis, methotrexate is the anchor disease-modifying drug (DMARD). When disease remains active despite an adequate methotrexate trial, the standard step-up is to escalate DMARD therapy rather than abandon it.
Step 2: The recommended next step is to add another conventional DMARD to methotrexate, building combination therapy. Sulfasalazine (often with hydroxychloroquine as triple therapy) is the classic add-on. Hence option d is correct.
Step 3: Simply continuing methotrexate and steroids (option b) does nothing new for ongoing active disease. Switching oral to parenteral methotrexate (option c) is a route change that does not constitute the standard escalation expected here.
Step 4: Anti-TNF agents are added when combination conventional DMARDs fail, and they are generally combined with methotrexate rather than used as monotherapy first, so option a is not the immediate next step. The answer is to add sulfasalazine.