A Study of Extending Relugolix Dosing Intervals Through Addition of Itraconazole or Ritonavir in Prostate Cancer Patients

Inclusion Criteria: Must have histologically or cytologically confirmed prostate cancer with plans to start medical castration therapy. Age 18 or older. Because no dosing or adverse event data are currently available on the use of relugolix in combination with itraconazole or ritonavir in patients <18 years of age, children are excluded from this study. Eastern Cooperative Oncology Group performance status ≤2 (Karnofsky ≥60%) Participants must satisfy the following laboratory criteria: Testosterone > 200 ng/dl QTc within normal limits Aspartate Transferase (AST)/alanine transaminase (ALT) < 3x upper limit of normal Ability to take oral medication and be willing to adhere to the medication regimen. Ability to understand and the willingness to sign a written informed consent document. Exclusion Criteria: Need for combination systemic therapy for prostate cancer including docetaxel and/or second-generation androgen receptor pathway targeted agents (i.e. abiraterone, enzalutamide, apalutamide, darolutamide, etc). Concurrent therapy with strong interacting drugs with CYP3A4 and P-gp (See Appendix list of strong inhibitors or inducers) due to concerning possible drug-drug interactions with itraconazole, ritonavir and relugolix. Potential drug-drug interactions will also be reviewed by study investigators prior to enrollment. History of allergic reactions attributed to compounds of similar chemical or biologic composition to relugolix, itraconazole or ritonavir. Patients receiving treatment with another investigational drug or other intervention within 3 expected half-lives of the agent. Serious or uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, unstable angina pectoris, or psychiatric illness/social situations that would limit compliance with study requirements. New York Heart Association Class III of IV congestive heart failure Known gastrointestinal malabsorption. Active psychiatric illness/social situations that would limit compliance with protocol requirements.