What is a potential consequence for "poor metabolizers" of codeine due to CYP2D6 activity?

Individuals identified as "poor metabolizers" of codeine due to reduced activity of the CYP2D6 enzyme are likely to experience inadequate pain relief. Codeine is a prodrug that requires metabolism by CYP2D6 into its active form, morphine, to exert its analgesic effects. When CYP2D6 activity is compromised or diminished, as in poor metabolizers, the conversion of codeine to morphine is significantly reduced. Consequently, these individuals may not achieve the expected pain relief from standard doses of codeine, as insufficient levels of the active metabolite are produced to effectively alleviate pain. This clinical scenario highlights the importance of genetic variability in drug metabolism and its implications for effective pain management.