• Rui V Duarte, Jon H Raphael, Mohammad S Haque, Jane L Southall, and Robert L Ashford.
• Faculty of Health, Birmingham City University, Birmingham, UK. ruivduarte@gmail.com
• Pain Physician. 2012 Sep 1;15(5):363-9.

BackgroundTolerance is defined as a phenomenon in which exposure to a drug results in a decrease of an effect or the requirement of a higher dose to maintain an effect. The fear of a patient developing opioid tolerance contributes regularly to the stigmatization and withholding of intrathecal opioid therapy for chronic pain of non-cancer origin.ObjectivesThe aim of this study was to describe the intrathecal opioid dose escalation throughout the years in chronic non-cancer pain patients. A secondary objective was the development of an intrathecal opioid dose predictive model.Study DesignRetrospective assessment of medical records.SettingDepartment of Pain Management, Russells Hall Hospital, Dudley, United Kingdom.MethodsMedical records were reviewed and pump refill notes screened from the date of implant through November 2010 for 31 patients undertaking continuous intrathecal opioid therapy. All the patients included had undertaken a minimum of 6 years of intrathecal therapy when the data were collected.ResultsSignificant increases in the intrathecal morphine dose were verified between follow-up at one year and all subsequent observations, F (2.075, 62.238) = 13.858, 0 < 0.001, but ceased to be significant from year 3 onwards, indicating stability of the morphine dose, F (3, 90) = 2.516, P = 0.63. A model that accounts for 76% of the variability of morphine doses at year 6 based on year 2 assessment combined with duration of pain prior to initiation of intrathecal therapy was developed: year 6 dose = -0.509 + (1.296 x [year 2 dose]) + (0.061 x [duration of pain]).LimitationsRetrospective study.ConclusionThe opioid dose escalation observed throughout the years was modest and not significant following year 3 of therapy. The model developed has the potential to assist the physician in the identification of a need for alternative treatment strategies. Furthermore, since many of the pump replacements are performed prior to year 6, it can also assist in the informed decision of the benefits and risks of the maintenance of this therapy.

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