IV PCA With or Without Continuous Dose vs Oral Opioid to Maintain Analgesia for Severe Cancer Pain After Successful Titration

Inclusion criteria

• Age 18 to 80 years;
• Histologically or cytologically confirmed malignant solid tumor;
• Persistent severe cancer-related pain (≥7 at rest on the 11-point numeric rating scale [NRS], where 0=no pain and 10=excruciating pain) in the 24 hours before screening;
• No radiotherapy to the painful area prior to randomization;
• No radiotherapy, chemotherapy, hormone therapy, targeted therapy, or bisphosphonate therapy within 7 days before randomization;
• Successful IPCA-HM titration within the past 24 hours;
• No history of psychiatric disorders;
• Ability to complete questionnaires;
• Ability to correctly understand and follow medication guidance from doctors and nurses;
• ECOG performance status ≤ 3;
• Provided written informed consent. Exclusion Criteria

• Patients with non-cancer-related pain; 2) Patients with paralytic ileus; 3) Patients with brain metastases; 4) Patients with hypersensitivity to morphine or hydromorphone; 5) Abnormal laboratory results: creatinine ≥ 2-fold of upper limit of normal (ULN) value, Alanine Aminotransferase (ALT) or Aspartate Aminotransferase (AST) ≥ 2.5-fold of the ULN value (≥ 5-fold for subjects with liver metastasis or primary liver cancer), or Child-Pugh class C liver function; 6) Patients unable to take oral medication; 7) Patients with uncontrolled nausea or vomiting; 8) Prior use of hydromorphone, morphine, or PCA devices within 14 days before screening; 9) Use of monoamine oxidase inhibitor drugs (MAOID) within the two weeks before randomization; 10) Women who are pregnant, lactating, or planning to be pregnant within one month after the trial completion; 11) Patients who abuse alcohol; 12) Patients with any other medical condition or reason, in the investigator's judgment, that would make them unsuitable to participate in the clinical trial.