Anesthetics Metabolism

The CYP3A4, CYP3A5, CYP2D6, and CYP2B6 family handles the bulk of anesthetic clearance, from propofol (CYP2B6) to fentanyl (CYP3A4) to codeine and tramadol (CYP2D6). Each enzyme runs on its own variant set, which is why one client can clear propofol quickly and codeine slowly, or vice versa.

Carriers of CYP2D6 reduced-activity variants ("poor metabolizers") are associated with significantly reduced effect from codeine (which depends on CYP2D6 for conversion to morphine) and prolonged effect from tramadol. Carriers of CYP2D6 high-activity variants ("ultrarapid metabolizers") are associated with the opposite pattern, and elevated risk of opioid toxicity from codeine. CYP3A5 expression status splits along ethnic lines and shifts intraoperative dosing meaningfully.

Co-administered medications and certain foods (grapefruit juice inhibits CYP3A4 for up to 72 hours) shift effective clearance further. Stress, recent illness, and liver function all influence enzyme activity acutely. Genotype-aware dosing, used routinely in some clinical contexts, meaningfully reduces complication rates.

Surgical anesthesia is the rare scenario where pharmacogenomics changes immediate, life-affecting outcomes. Which CYP combination you carry decides whether standard dosing fits or whether the anesthesia team has reason to adjust, information that belongs in the conversation before any planned procedure.