Cytochrome P450 2C9 phenotyping using low-dose tolbutamide.

OBJECTIVES: The hypoglycaemic drug tolbutamide is used for assessment of CYP2C9 activity in vivo. However, therapeutically active doses of 500 mg bear the risk of hypoglycaemia, and a tolbutamide-derived parameter based on a single plasma or urine concentration reflecting CYP2C9 activity accurately is lacking. METHODS: We examined tolbutamide and its metabolites 4'-hydroxy-tolbutamide and carboxytolbutamide in plasma and urine of 26 healthy, male volunteers up to 24 h after intake of 125 mg tolbutamide using liquid chromatography-tandem mass spectrometry. CYP2C9 genotypes were determined by sequencing of exons 3 and 7. Raw plasma and urine data were compared with pharmacokinetic parameters, CYP2C9 genotypes, and data from a study in 23 volunteers with all six CYP2C9*1-*3 combinations who received 500 mg tolbutamide. RESULTS: Plasma clearance and tolbutamide plasma concentrations 24 h after drug intake reflected the genotypes: 0.85 l/h and 1.70 microg/ml (95% confidence interval, CI, 0.80-0.89 l/h and 1.50-1.90 microg/ml) for CYP2C9*1 homozygotes (n=15), 0.77 l/h and 2.14 microg/ml (95%CI, 0.67-0.88 l/h and 1.64-2.63 microg/ml) for *1/*2 genotypes (n=7), 0.60 l/h and 3.13 microg/ml (95%CI, 0.58-0.62 l/h and 2.68-3.58 microg/ml) for *1/*3 genotypes (n=3), and 0.57 l/h and 3.27 microg/ml in the single *2/*2 carrier. Natural logarithms of tolbutamide plasma concentrations 24 h after intake correlated to plasma clearance (r(2)=0.84, P<0.0000001). This correlation was confirmed in the comparison data set (r(2)=0.97, P<0.0000001). CONCLUSIONS: A low dose of 125 mg tolbutamide can safely and accurately be used for CYP2C9 phenotyping. As a simple metric for CYP2C9 activity, we propose to determine tolbutamide in plasma 24 h after drug intake.

Acrylamide: increased concentrations in homemade food and first evidence of its variable absorption from food, variable metabolism and placental and breast milk transfer in humans.

We have developed a liquid chromatography/mass spectrometry (LC-MS/MS) assay to determine acrylamide in various body fluids. The assay also allows the reliable quantitation of acrylamide in food. In a total of 11 healthy male and female subjects, we were able to show that acrylamide from food given to humans is in fact absorbed from the gut. The half-lives determined in two male subjects were 2.2 and 7 h. Acrylamide was found in human breast milk and penetrated the human placenta (n = 3). The variability of acrylamide concentrations found in this investigation is most likely caused by variable intersubject bioavailability and metabolism. This may be an important indication that the assessment of the risk from acrylamide for the individual may be very difficult without knowing the concentrations of acrylamide in the body. This should be considered in the design of any risk assessment study or post hoc analysis of earlier studies. At this time, we suggest that pregnant women and breast-feeding mothers avoid acrylamide-containing food.