An Extension Study of Methylnaltrexone Bromide (MNTX) in Participants With Advanced Pancreatic Cancer

Inclusion Criteria: * Adult participants greater than or equal to (≥)18 years of age on the date the Informed Consent Form (ICF) is signed, with the capacity to provide voluntary informed consent. * Enrolled in double-blind Study SAL-REL-2042 (NCT04083651) and completed an end of study (EOS) visit (Day 168) or completed Day 56 of the Study SAL-REL-2042 (NCT04083651). * Must be able to read, understand, and provide written informed consent on the Institutional Review Board (IRB)-approved ICF and provide authorization, as appropriate, for local privacy regulations. * Willing and able to comply with scheduled visits, the treatment plan, and laboratory tests. * Signed an informed consent/Health Insurance Portability and Accountability Act (HIPAA) form. Exclusion Criteria: * Concurrent therapy with any other investigational agent during the study. * Current use of a peripherally acting mu-opioid-receptor antagonist. * Current evidence of untreated brain metastasis(es). * Diarrhea greater than Grade 1, based on the National Cancer Institute Common Terminology Criteria for Adverse Events Version 5.0 (NCI-CTCAE v5.0). * Bowel obstruction. * Advanced liver disease. * Renal disease. * Any other severe, acute, or chronic medical or psychiatric condition or laboratory abnormality that may increase the risk associated with study participation or study drug administration, or may interfere with the interpretation of study results, and in the judgment of the Principal Investigator, would make the participant inappropriate for the study.