A 32-year-old male from Mumbai presents on day 4 of fever (39.5°C), with myalgia, arthralgia, and a maculopapular rash on trunk and limbs. Platelet count is 95,000/µL, haemoglobin 14 g/dL, and WBC 3,200/µL. Dengue NS1 antigen is positive. He denies bleeding manifestations and has normal vital signs. What is the most appropriate immediate next step in management?