Conditions: Pain Chronic Pain Hyperalgesia
Keywords: Pain Chronic pain Opioid induced hyperalgesia Opioid therapy
Allocation: RANDOMIZED | Intervention model: PARALLEL
Enrollment: 79
Healthy volunteers: no

Brief summary:
The purpose of this study is to compare pain threshold, pain tolerance, and wind up, as measured by QST, before and after a single dose of ketamine infusion under two clinical conditions: chronic pain patients on opioid therapy and chronic pain patients without opioid therapy.

Detailed description:
We hypothesize that:

1. Chronic pain patients on chronic opioids would have a lower pain threshold and lower pain tolerance when compared to opioid naïve patients (patients with chronic pain with non-opioids treatment)., as measured by QST in a non-affected neutral limb;
2. Chronic pain patients on chronic opioids would have an increased response to painful stimulation, so called "windup" as demonstrated by QST;
3. Both "wind-up" and altered pain threshold and tolerance would be indicative of the presence of opioid-induced hyperalgesia;
4. Intravenous ketamine, an NMDA receptor antagonist, could be used to differentiate between opioid-induced hyperalgesia and opioid tolerance.

Arms:
arm 1: This group consists of 16 subjects who have chronic pain conditions treated with an opioid regimen. Subjects were randomized to receive a ketamine treatment during the study. They were given an intravenous infusion of ketamine (0.05mg/kg) diluted in 50 ml normal saline over 30 minutes. arm 2: This group consists of 22 subjects who have chronic pain conditions but were not on an opioid regimen over the last 3 months. Subjects were randomized to receive a ketamine treatment during the study. They were given an intravenous infusion of ketamine (0.05mg/kg) diluted in 50 ml normal saline over 30 minutes. arm 3: This group consists of 18 subjects who have chronic pain conditions treated with an opioid regimen. Subjects were randomized to receive a placebo treatment during the study. They were given an intravenous infusion of 50 ml normal saline over 30 minutes. arm 4: This group consists of 23 subjects who have chronic pain conditions but were not on an opioid regimen over the last 3 months. Subjects were randomized to receive a placebo treatment during the study. They were given an intravenous infusion of 50 ml normal saline over 30 minutes.

Interventions: intervention 1: Ketamine intervention 2: Placebos
Intervention descriptions: intervention 1: To compare pain threshold, pain tolerance, and wind up, as measured by QST, before and after a single dose of ketamine infusion under two clinical conditions: chronic pain patients on opioid therapy and chronic pain patients without opioid therapy. intervention 2: To compare pain threshold, pain tolerance, and wind up, as measured by QST, before and after a single dose of ketamine infusion under two clinical conditions: chronic pain patients on opioid therapy and chronic pain patients without opioid therapy.

Protocol document: