Intravenous vs Oral Analgesia in Cancer Patients With Severe Pain After Successful Titration

Inclusion Criteria: 1. The patients were 18-80 years old and diagnosed as malignant tumor by pathology; 2. Patients with cancer pain is NRS pain score ≥ 7 during previous 24 hours; 3. Patients who will not be treated with radiotherapy within 7 days prior to randomization and during study ; 4. Patients who need chemotherapy, long term administration of hormone, targeted therapy, or bisphosphonates therapy should undergo a stable anti- tumor therapy prior to randomization ; 5. Patients or his/her caregivers who are able to fill out the questionnaire forms ; 6. Ability to correctly understand and cooperate with medication guidance of doctors and nurses ; 7. Without psychiatric problems; 8. ECOG performance status ≤3; 9. Not participated in another drug clinical trial within one month before inclusion（including hydromorphone）; 10. The subjects voluntarily signed the informed consent. Exclusion Criteria: 1. The pain is confirmed not due to cancer; 2. Patients with severe post-operative pain; 3. Patients with paralytic ileus; 4. Patients with brain metastasis; 5. Patients hypersensitive to opioids; 6. Patients with abnormal lab results that have obvious clinical significance, such as creatine ≥ 2 fold of upper limit of normal value, alanine aminotransferase (ALT) or aspartate aminotransferase (AST) ≥ 2.5 fold of upper limit of normal value, or liver function of Child C grade; 7. Patients who cannot take drugs orally; 8. Patients with an incoercible nausea or vomiting; 9. Those who have received monoamine oxidase inhibitor (MAOI) within two weeks before randomization; 10. Patients who are pregnant or in lactation, or who plan to be pregnant within one month after the trial; 11. Those with opioid addiction; 12. Alcoholic patients; 13. Those with cognitive dysfunction; 14. Those with severe depression; 15. Patients with other conditions or reasons causing the patients unable to complete the clinical trial.