Dornase Alfa and Urokinase for Kids With Pleural Empyema

Inclusion Criteria: * Age \> 1 year and \< 16 years * Respiratory infection (pneumonia or lung abscess) * Effusion occupying at least 1/3 of hemithorax on chest X-ray * Complicated effusion (presence of at least one of the following): * Hyperechoic pleural fluid on chest US scan * Loculated collection on chest US or CT scan * Purulent pleural fluid * Positive culture or Gram stain on pleural fluid Exclusion Criteria: * Non parapneumonic effusion * Immunodeficiency * Neurological impairment * Suspected or proven allergy to Urokinase or Dornase alfa * Suspected or documented bronchopleural fistula * Impaired coagulation (INR\>2), haemorrhage, high risk for bleeding * Thoracic surgical procedure (e.g. thoracoscopy, mini-thoracotomy) already performed * Chest drain inserted since 6 or more days