title: Microdose pharmacogenetic study of ¹⁴C-tolbutamide in healthy subjects with accelerator mass spectrometry to examine the effects of CYP2C9∗3 on its pharmacokinetics and metabolism.
abstract: Microdose study enables us to understand the pharmacokinetic profiles of drugs in humans prior to the conventional clinical trials. The advantage of microdose study is that the unexpected pharmacological/toxicological effects of drugs caused by drug interactions or genetic polymorphisms of metabolic enzymes/transporters can be avoided due to the limited dose. With a combination use of accelerator mass spectrometry (AMS) and (14)C-labaled compounds, the pharmacokinetics of both parent drug and its metabolites can be sensitively monitored. Thus, to demonstrate the usability of microdose study with AMS for the prediction of the impact of genetic polymorphisms of CYP enzyme on the pharmacokinetics of unchanged drugs and metabolites, we performed microdose pharmacogenetic study using tolbutamide as a CYP2C9 probe drug. A microdose of (14)C-tolbutamide (100 μg) was administered orally to healthy volunteers with the CYP2C9(∗)1/(∗)1 or CYP2C9(∗)1/(∗)3 diplotype. Area under the plasma concentration-time curve for the (14)C-radioactivity, determined by AMS, or that for the parent drug, determined by liquid chromatography/mass spectrometry, was about 1.6 times or 1.7 times greater in the CYP2C9(∗)1/(∗)3 than in the CYP2C9(∗)1/(∗)1 group, which was comparable to the previous reports at therapeutic dose. In the plasma and urine, tolbutamide, carboxytolbutamide, and 4-hydroxytolbutamide were detected and practically no other metabolites could be found in both diplotype groups. The fraction of metabolites in plasma radioactivity was slightly lower in the CYP2C9(∗)1/(∗)3 group. Microdose study can be used for the prediction of the effects of genetic polymorphisms of enzymes on the pharmacokinetics and metabolic profiles of drugs with minimal care of their pharmacological/toxicological effects.
authors.affiliation: Yokohama College of Pharmacy, 601 Matanocho, Totsuka-ku, Yokohama 245-0066, Japan. toshihiko_ikeda-san@nifty.com
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Ikeda
authors.forename: Shinsuke
authors.initials: S
authors.lastname: Aoyama
authors.forename: Zenzaburo
authors.initials: Z
authors.lastname: Tozuka
authors.forename: Kohei
authors.initials: K
authors.lastname: Nozawa
authors.forename: Yoshimi
authors.initials: Y
authors.lastname: Hamabe
authors.forename: Takao
authors.initials: T
authors.lastname: Matsui
authors.forename: Michiko
authors.initials: M
authors.lastname: Kainuma
authors.forename: Setsuo
authors.initials: S
authors.lastname: Hasegawa
authors.forename: Kazuya
authors.initials: K
authors.lastname: Maeda
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Sugiyama
mesh_terms: D000328:Adult; D001189:Aryl Hydrocarbon Hydroxylases / Q000235:genetics* / Q000378:metabolism; D002250:Carbon Radioisotopes / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics / Q000652:urine; D065729:Cytochrome P-450 CYP2C9; D005243:Feces / Q000737:chemistry; D005838:Genotype; D006801:Humans; D007004:Hypoglycemic Agents / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics* / Q000652:urine; D008297:Male; D013058:Mass Spectrometry / Q000379:methods; D008875:Middle Aged; D011110:Polymorphism, Genetic; D014044:Tolbutamide / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics* / Q000652:urine; D055815:Young Adult
chemical_list: D002250:Carbon Radioisotopes; D007004:Hypoglycemic Agents; D014044:Tolbutamide; C450260:CYP2C9 protein, human; D065729:Cytochrome P-450 CYP2C9; D001189:Aryl Hydrocarbon Hydroxylases
keywords: Accelerator mass spectrometry (AMS); CYP2C9; Genetic polymorphism; Microdose; Tolbutamide