How does CYP2D6 genotype affect tramadol efficacy and safety?

• A. Converts tramadol to active M1 metabolite; poor metabolizers have reduced analgesia, ultrarapid metabolizers risk toxicity.
• B. Has no effect on tramadol efficacy or safety.
• C. Only affects urinary excretion of tramadol.
• D. Increases hepatic metabolism of tramadol only in poor metabolizers.

Answer: (A)

CYP2D6 variation changes how tramadol is activated because tramadol itself is a prodrug whose analgesic effect mainly comes from its active metabolite M1 (O-desmethyltramadol) formed by CYP2D6. In people with poor metabolizer status, CYP2D6 activity is reduced or absent, leading to little M1 formation and thus weaker analgesia despite standard dosing. In ultrarapid metabolizers, CYP2D6 activity is high, producing excess M1, which enhances μ-opioid receptor stimulation and markedly increases the risk of opioid-related toxicity, including respiratory depression and severe sedation. This genotype-directed difference in conversion explains both efficacy and safety variations with tramadol. The other statements don’t fit because CYP2D6 does not primarily govern urinary excretion, and there is a meaningful effect on tramadol’s action through M1 formation, not a lack of effect overall.