Long-term consequences of acute pain for patients under methadone or buprenorphine maintenance treatment.

Background: Acute and chronic pains are reported to be highly prevalent in patients under opioid maintenance treatment (OMT). Lack of knowledge concerning the complex relationship between pain, opioid use, and their impact on OMT efficacy can account for the barriers encountered for pain management.
Objectives: To assess the impact of acute pain exposure on long-term OMT retention in a cohort of patients under buprenorphine or methadone followed up during 12 months.
Study Design: Prospective, multi-center observational cohort clinical study.
Setting: Emergency departments, surgery departments, and specialized addiction care centers in an outpatient setting in south-western France (Midi-Pyrenees area), from April 2008 to January 2010.
Methods: Patients aged 18 or more under OMT for at least 3 months, and followed up by a physician were recruited. Acute pain was assessed using the Visual Analog Scale (VAS) or the Verbal Rating Scale (VRS). Exposed patients were those with a pain score greater than 0 at the time of admission on any of the rating scales. The OMT rate after 12 months was compared among exposed and unexposed patients. OMT retention was also investigated after 3 and 6 months follow-up.
Results: A total of 151 patients, 81 exposed and 70 unexposed, were recruited; among them, respectively, 26 (32%) and 34 (49%) completed 12-months follow-up. Acute pain exposure appeared to be significantly and negatively associated with retention in treatment (crude OR: 0.44; 95% CI [0.22 - 0.87]; adjusted OR: 0.46; 95% CI [0.23 - 0.93]). Compared to methadone users, patients under buprenorphine were less likely to have their OMT maintained after 12 months (OR 0.37; 95% CI [0.18 - 0.75]; adjusted OR 0.38; 95% CI [0.18 - 0.80]).
Limitations: Follow-up rate was 40% (60/151).
Conclusion: This study demonstrates the strong negative impact of acute pain on OMT in a population mainly composed of patients under buprenorphine, as well as differential response depending on the OMT medication. The findings highlight the need to consider the characteristics of pain in the population under OMT and to develop evidence-based guidelines for pain management.
Trial Registration: The study was registered at www.clinical.trials.gov with the study identifier: NCT00738036. Ethics Committee approval was received on February 11, 2008. Participants' written consent was not required.