45-year-old patient complains of cramping abdominal pain, tenesmus, and frequent liquid stools with blood. The disease onset was 5 years ago. Objectively, the following is observed: body temperature 37.5°C, blood pressure 110/60 mm Hg, pulse - 98/min, the abdomen is soft, painful during palpation along the course of the large intestine. Irrigography results: the large intestine is narrowed, the haustra are absent, the contours are uneven and indistinct. Complete blood count: erythrocytes 3.2 * 1012/L, hemoglobin 110 g/L, color index 0.85, leukocytes 8.1 * 109/L, band neutrophils - 5%, lymphocytes 30%, monocytes 3%, eosinophils 3%, segmented neutrophils 59%, ESR 24 mm/hour. Fecal calprotectin - 95 units. What drug must be prescribed first in this case?