AIMS: ), calculated from urinary 6-hydroxymelatonin (6-O-MEL) excretion and plasma melatonin (MEL) exposure, as a potential endogenous marker of CYP1A2 activity and compared it with caffeine (CA)-based indexes. METHODS: was calculated as urinary 6-hydroxymelatonin excretion divided by the corresponding plasma melatonin AUC. RESULTS: (r = 0.57 and 0.67) and plasma paraxanthine/CA (PX/CA) ratios (r = 0.63 and 0.65). CONCLUSIONS: correlates with established caffeine-derived CYP1A2 phenotyping indexes and may represent a probe-free approach for CYP1A2 phenotyping. Further validation under CYP1A2 induced and inhibited conditions is warranted.
Yokokawa et al. (Thu,) studied this question.