CYP2C19 and CYP2D6 phenotyping results in a Dutch population (Tamminga et al., 1999)
The population investigated mainly comprised Caucasian (98.9%) male (68%) volunteers mainly from the northern part of The
Netherlands. Of the total population 0.5% was Negroid and 0.6% was of Oriental origin, excluded in the results below.
Volunteers: 4301 unrelated subjects (3299 males and 1002 females) were evaluated:
Phenotyped for CYP2D6: 1663 subjects (1469 males and 194 females).
Phenotyped for both CYP2D6 and CYP2C19: 2638 subjects (1830 males and 808 females).
CYP2C19 phenotyping results:
The urinary (R)-mephenytoin and (S)-mephenytoin excretion ratio was used as metabolic ratio. Subjects with S/R ratios > 0.8
were classified as poor metabolisers, whilst subjects with ratios <0.8 were classified as extensive metabolisers.
Dutch caucasians (n= 2613, healthy volunteers)
Poor metabolisers: 1.8 %
Extensive metabolisers: 98,2 %
The metabolic ratios in females are 20% lower for CYP2D6. This indicates a significantly increased activity for CYP2D6 in females compared with males.
Oral contraceptive use significantly decreased the CYP2C19 activity by 68%.
CYP2D6 phenotyping results:
Urinary dextromethorphan/dextrorphan ratio was used as an indication for metabolic activity. Subjects
with metabolic ratios > 0.3 were classified as poor metabolizers (PM) and metabolic ratios <0.3 were classified as extensive metabolizers (EM)
Dutch caucasian (n=4252, healthy volunteers):
Poor metabolisers: 8.0 %
Extensive metabolisers: 92.0 %
The metabolic ratios in females are 20% lower for CYP2D6. This indicates a significantly reduced activity for CYP2C19 in females compared with males.
[Note editor: Study-population is allocated into two categories: extensive or poor metabolizers; superextensive and slow metabolizers are not mentioned.
Apparently extensive and superextensive are lumped together into ‘extensive metabolizers’ and slow and poor metabolizers into ‘poor metabolizers’]