A 16-year-old male presents with pain and swelling in the right thigh after a bicycle fall. Examination reveals a 10cm × 8cm hematoma in the upper right thigh with marked tenderness. Laboratory tests: normal bleeding time, clotting time 14 minutes, APTT prolonged by 20 sec compared to control, not corrected by normal BaSO<sub>4</sub>-adsorbed plasma but corrected by normal serum. What is the first-line treatment?