COGNITIVE AND MOTOR FUNCTION IMPAIRMENTS DURING CONTINUOUS OPIOID ANALGESIC INFUSIONS

Morphine and other opioid analgesics may interfere with normal cognition and motor function during long-term treatment of cancer-related pain. In this study, we used individually tailored steady-state drug infusions to control plasma concentrations of morphine and alfentanil and measured the extent of cognitive and motor impairments produced by each drug in healthy volunteers. The tailored infusions allowed evaluation of cognitive and motor effects at three sequential, steady plasma concentrations of each opioid. During continuous infusion, both drugs caused significant, plasma concentration-related impairments of ability to process serially-presented information and of fine motor control at plasma drug concentrations within the usual therapeutic range. We found significant relationships between cognitive and motor function decrements and plasma opioid concentration with both morphine and alfentanil. We conclude that magnitudes of cognitive and motor function impairments are equivalent for these two mu receptor selective agonists at equianalgesic plasma concentrations.