Background: Sickle cell disease (SCD) is the most common inherited blood disorder in the United States (US), affecting approximately 100,000 individuals in the country who are primarily of African descent. One of the most prevalent complications of SCD is pain as a result of episodic vaso-occlusive crises. Over time, many individuals with SCD develop chronic pain and opioid dependence for pain management. L-glutamine (EndariTM) was approved by the US Food and Drug Administration in 2017 for patients 5 years-old and older to reduce complications from SCD after reviewing a phase-III placebo-controlled trial. In this study, L-glutamine led to a reduction in median number of pain crises and increased time to first pain crisis when compared to placebo (Niihara et al, NEJM, 2018). However, the impact of L-glutamine on opioid use over time remains unknown. In this study, we evaluated the effect on opioid use in individuals who were started on L-glutamine for worsening SCD related pain.
Methods: After institutional review board approval, we retrospectively reviewed the electronic medical record (EMR) of individuals with SCD followed at the University of North Carolina Pediatric and Adult Sickle Cell clinics prescribed L-glutamine in 2018-2019 for worsening acute and chronic SCD-related pain. The North Carolina state controlled substance reporting system, an online clinical tool which collects information on dispensed controlled substance prescriptions to patients that is freely available to prescribers, was also reviewed for filled opioid prescriptions (and milligram morphine equivalents - MME) for each patient. Data, including health care utilization (e.g. hospitalizations and emergence room (ER) visits) and hemoglobin levels for each patient were also evaluated in the EMR for the four months preceding and the four months after L-glutamine was started to determine if changes were sustained.
Results: We identified four female patients (ages ranging from 9 to 24 years-old) with SS genotype and chronic pain with acute exacerbations who had significant opioid prescription reduction after starting L-glutamine. Three individuals were taking the maximum tolerated dosing of hydroxyurea and experiencing escalating pain crises prior to initiation of L-glutamine. One patient was intolerant of hydroxyurea and was on a chronic transfusion program for chronic pain management when she was started on L-glutamine for worsening chronic pain. All patients, or caregivers, reported a reduction in acute on chronic pain after initiating L-glutamine. Each patient had a reduction in 4-month total opioid prescription use (in MME) after starting L-glutamine, ranging from a 21% reduction to 100% reduction (Figure 1). Heath care utilization significantly decreased in 1 patient after starting L-glutamine, with 3 ER visits and 2 hospitalizations in the pre-treatment period and no ER visits or hospitalizations in the post-treatment period. There was no difference in the average hemoglobin levels pre-and-post L-glutamine initiation among the patients (9.8g/dL vs. 9.7g/dL).
Discussion: L-glutamine appears to have some benefit in reducing pain and opioid use, as well as healthcare utilization, in a subset of patients with SCD and chronic pain. Although we evaluated a small number of patients, all individuals (or caregivers) reported decreased pain very soon after starting L-glutamine. One patient stopped opioid use altogether in the time period evaluated. Future studies should investigate if effectiveness of L-glutamine may be based on unique red cell metabolic profiles, SCD genotype, or timing of drug initiation in these and similar patients. Future investigations will also determine long-term tolerability of L-glutamine and if the reduction in opioid use is sustained for longer periods among these patients and other responders.
Carden:GBT: Honoraria; NIH: Research Funding.
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