J. Wieling et al., Evaluation of analytical and clinical performance of a dual-probe phenotyping method for CYP2D6 polymorphism and CYP3A4 activity screening, THER DRUG M, 22(4), 2000, pp. 486-496
A bioanalytical method for the determination of dextromethorphan (DEX) and
its metabolites dextrorphan (DTX), 3-methoxymorphinan (3MM), and 3-hydroxym
orphinan (3HM) in human urine was developed for CYP2D6 phenotyping and CYP3
A4 activity measurements in clinical pharmacology studies using dextrometho
rphan administered in a drinking solution as substrate. The method was eval
uated by thorough conventional validation and by a cross-validation of the
method with a previously applied method for dextromethorphan and dextrorpha
n only (CYP2D6 phenotyping). Cross-validation with the former method showed
no significant differences in measured concentrations of volunteer samples
. This guaranteed the consistency of epidemiologic data in the database col
lected from two methods. For the CYP2D6 and CYP3A4 evaluations, the clinica
l parameters are ratios of concentrations. It appeared that severe variance
in individual concentrations generally did not infltrence the variance of
ratios significantly, because experimental errors in concentrations of two
analytes proved to correlate considerably. For CYP2D6 values around the ant
imodes, the chance of a misclassification is very small. The chance of clas
sifying an extensive metabolizer as a poor metabolizer or vice versa is neg
ligible. For CYP3A4 activity determinations it was concluded that in genera
l a change in dextromethorphan/3-methoxymorphinan (DEX/3MM) ratios of 10% o
r more as detected with the current method, is a significant increase or de
crease in the activity of CYP3A4. The authors concluded that they had obtai
ned an analytically valid and clinically reliable bioanalytical method for
the determination of dextromethorphan and its metabolites dextrorphan, 3-me
thoxymorphinan, and 3-hydroxymorphinan in human urine for CYP2D6 phenotypin
g and CYP3A4 activity measurements for clinical pharmacology studies.