A 40-year-old male was admitted for intestinal tuberculosis with tuberculous peritonitis. Treatment with isoniazid (INH), rifampin, and others led to gradual improvement. Over the past 2 days, he developed constipation, vomiting, and abdominal distension. Physical exam: distended abdomen with visible intestinal loops and peristaltic waves, hyperactive bowel sounds. Abdominal X-ray shows multiple air-fluid levels. Persistent gastrointestinal decompression showed no improvement. The next step in management is: