Measurement of debrisoquine and 4-hydroxydebrisoquine in urine by liquid chromatography

Frequency of human CYP2D6 mutant alleles in a normal Chinese population

Substantial differences in the pharmacogenetics of debrisoquine hydroxylation exist between Caucasians and Chinese populations. Among Chinese, not only is the frequency of the poor metabolizer phenotype low, the contribution of the 29B mutation in the CYP2D6 gene is insignificant. By contrast the frequency of D6-J is very common (approximately 0.6) and is clearly related to the activity of debrisoquine hydroxylase. Its presence however, does not predict the poor metabolizer phenotype. The D6-C mutation was also not detectable in our population.

Evidence for the polymorphic oxidation of debrisoquine in the Thai population

Debrisoquine polymorphism has been studied extensively in Caucasian populations. The prevalence of the poor metaboliser phenotype is 3-10% in European and American Caucasian populations but appears to be very low in Asian populations. This study was carried out to determine the metabolic oxidation status in 173 Thai subjects. Phenotyping was performed using the metabolic ratio (MR) calculated as the 0-8 h urinary output of debrisoquine/0-8 h urinary output of 4-hydroxydebrisoquine after oral administration of 10 mg debrisoquine hemisulphate. Two subjects (1.2%) were phenotyped as poor metabolisers; they had MR values of 13.17 and 92.04. The incidence of the poor metaboliser phenotype of debrisoquine oxidation of 1.2% seems to be lower in the Thai population compared with that in various Caucasian populations.

Oxidation phenotyping in Chinese and Malay populations

1. Debrisoquine hydroxylation phenotyping was carried out in 97 Chinese and 97 Malay healthy volunteers. 2. No poor metabolizer was found in the Chinese population. Using a metabolic ratio antimode of 10.0, two poor metabolizers were present amongst the Malays studied.

Diurnal effects on debrisoquine hydroxylation phenotyping

A study was performed to show whether debrisoquine phenotyping could be performed as an overnight procedure. Phenotyping of 33 normal volunteers was carried out during the day and night. A good correlation was observed between the day- and night-time metabolic ratios, although wide variation was observed in 3 subjects.