Relationship between serum methadone concentration and cold pressor pain sensitivity in patients undergoing methadone maintenance therapy

Hyperalgesia is a common clinical phenomenon among opioid dependent patients on methadone maintenance therapy (MMT) and it may be associated with undertreated pain and/or therapeutic failure. This study aimed to investigate association between serum methadone concentration (SMC) and cold pressor pain responses. Cold pressor pain responses in 147 opioid dependent patients on MMT were assessed using cold pressor test (CPT) at 0 hour and at 2, 4, 8, 12, and 24 hours after the dose intake. Blood samples were collected at 24 hours after the dose. Serum methadone concentrations were measured using the Methadone ELISA kit and classified into two categories: 0.05). Our results suggest an association of trough methadone concentration with the cold pressor pain threshold among opioid dependent patients on MMT. It would be useful to study the mechanisms underlying this association to help managing pain in such a population.