Acute Pain Management in Patients on Opioid Replacement Therapy

Eligible participants will have 8 sessions where they will receive two IM injections.The dose of ketamine will be manipulated (0 mg/kg to 0.4 mg/kg) across sessions. The dose of hydromorphone will either be 0 mg or 8 mg. Therefore, participants will be exposed to ascending doses of ketamine with and without hydromorphone. Order of study medications will be randomized for each participant by an un-blinded statistician and transmitted securely to study pharmacist in charge of medication administration. This study will provide unique information on optimal hydromorphone-ketamine dosing strategies for acute pain management. in buprenorphine maintained patients. Each session will take place 17 hours after the last buprenorphine dose (trough levels) to control for time since last dose. Sessions will be held on a dedicated unit for human subjects clinical research at Zuckerberg San Francisco General and include two IM injections of study medication given 15 minutes apart by blinded nursing staff. Study sessions will each last approximately 5 hours. Sessions will take place 1-2x weekly and must be separated by at least 72 hours to allow for drug wash-out. QST outcomes will be measured at baseline, as well as 15, 75, 135, and 195 minutes after injection #2 for each session. In addition, abuse liability outcomes will be measured at baseline (if required) and at 15, 75, 135, and 195 minutes after injection #2 for each session. Blood will be drawn to evaluate baseline buprenorphine /norbuprenorphine levels. Then, PK analyses will be done for ketamine, norketamine and hydromorphone. Blood will be drawn at baseline as well as 15, 75, 135, and 195 minutes after injection #2. Primary outcome will be analgesia as assessed by QST. The use of various QST measures which assess acute anti-nociception as well as central modification of pain processing will allow us to evaluate whether overall analgesia results from blocking of nociceptor signaling and/or changes to central pain facilitation to better understand the mechanism of ketamine-hydromorphone combinations.