Cognitive function in chronic non-malignant pain patients treated with sustained-release morphine sulfate (Avinza)
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The purpose of this study is to evaluate the association between sustained-release morphine (Avinza®), and performance on neuropsychological tests assessing short term memory, information processing, and motor skills in chronic pain patients, while controlling for stages of pain model variables and the effects of benzodiazepines. A convenience sampling procedure was utilized to enroll a sample of patients who had a trial of short-acting narcotic analgesics for their chronic non-malignant pain. Enrolled patients were treated with long-acting morphine Avinza.® Patient interviews were conducted at enrollment and one-month follow-up. A total of 129 patients were enrolled in the study. Mean pain intensity ratings at the highest, lowest, and average levels in the previous week were lower at follow-up (10.90, 4.56. 7.64) than at baseline (12.71, 6.76, 10.01) respectively. Reduction in pain levels was associated with a corresponding reduction in levels of pain unpleasantness, pain suffering, and pain behaviors. The models evaluating the associations between the stages of pain model variables, morphine dose, benzodiazepine dose, and digit span test (chi square = 147.79, p = 0.76), digit symbol test (chi square = 128.06, p = 0.5), and paced auditory serial attention test fit the data well (chi square = 160.39, p = 0.85). There was a statistically significant inverse association between frequency of pain behaviors and digit span test scores at baseline (-0.49, p = 0.01). Although the association between pain behaviors and digit symbol test scores (- 17. 0 %, p = 0.09) and paced auditory serial addition test scores (-4.0%, p = .28) at baseline were not statistically significant, a large negative effect was found. At follow-up, the association between pain behaviors and digit span test was positive and not significant. The negative association between frequency of pain behaviors and digit symbol test scores (-4.4%, p = 0.67 ) and paced auditory serial addition test scores (-2.8%, p = 0.21) at follow-up were considerably weaker. There were no significant association between opioid dose and cognitive function test scores. Opioid therapy, particularly, sustained release morphine therapy (Avinza) does not contribute to cognitive impairment in chronic pain patients.