The Correlation Between Oral Opioid and Intrathecal Opioid Dosages for Controlling Chronic Pain

Introduction: In chronic pain, there is a general tendency of progressive increase in oral opiate dosing over time for adequate pain control. Lower-dose intrathecal morphine delivery is a promising alternative to oral opiates, improving quality of life and reduicing opiate related mortality and morbidity.

Methods: This retrospective study included 32 consecutive intrathecal drug delivery morphine pump procedures performed at St. James Hospital, UR, NY during the period of Dec. 2015 to Dec. 2019. All patients were on one or more oral opioids prior to intrathecal conversion. After patient selection, intrathecal morphine trial was performed and if there was more than a 60% reduction in pain symptoms using 0-10 numeric pain rating scale, a protocol was developed to wean patients off oral opioids over 2-4 weeks, before a permanent intrathecal drug delivery pump was implanted. The intrathecal drug delivery pump was programmed to deliver low dose 0.06-0.6 mg of morphine over 24 hours in a simple continuous or flexible mode. The oral daily morphine dose and Morphine mg equivalent (MME) were calculated for each patient before intrathecal morphine trial and it was correlated with daily Intrathecal morphine dose.

Results: Thirty two patients were selected (17 male, 15 female). The age range was 39 to 81 years with mean 60 years. The follow up period was 5 years. All 32 patients had adequate pain control with intrathecal drug delivery at 5 years (80-100% pain reduction to baseline). There was no significant correlation between starting oral MME and final intrathecal morphine dosing (p > 0.05).

Conclusion : Low dose intrathecal morphine proved effective at long-term pain control after conversion from oral opiates in patients with chronic pain. We did not find a significant correlation between daily oral morphine or morphine mg equivalent dose and daily intrathecal morphine dose. Thus, adequate pain control can be achieved with lower doses of intrathecal morphine. This study further supports the potential benefits of intrathecal morphine delivery in management of chronic pain.