¹Department of Medical Laboratory Sciences and Technology, Division of Clinical Pharmacology, Karolinska Institutet at Huddinge University Hospital, Stockholm; and the Department of Pharmacology and Psychiatry, Medical School, University of Extremadura, Badajoz.

Correspondence: Marja-Liisa Dahl, MD, PhD, Department of Medical Sciences, Clinical Pharmacology, University Hospital, SE-75185, Uppsala, Sweden. E-mail: Marja-Liisa.Dahl@medsci.uu.se

^*Supported by grants from the Swedish Medical Research Council (3902), the Swedish Society of Medicine, and the Karolinska Institutet. Dr Yasar is the recipient of a Turkish Higher Education Council PhD scholarship, and Dr Eliasson is the recipient of a Merck Sharp & Dohme fellowship in clinical pharmacology. The Spanish study and fellowship of Mr Dorado were supported by the Ministry of Health, Spain (Instituto Carlos III, Fis01/0699).

Received 21 March 2001; Accepted 17 October 2001.

Abstract

Background And Aim: Losartan is metabolized by polymorphic CYP2C9 to E-3174. Our aim was to evaluate the pharmacokinetics of losartan and E-3174 in relation to the CYP2C9 genotype.

Methods: A 50-mg oral dose of losartan was given to 22 Swedish volunteers with different CYP2C9 genotypes. Losartan and E-3174 were analyzed by HPLC in plasma and urine samples collected up to 24 hours after drug intake. Furthermore, losartan and E-3174 were analyzed in 8-hour urine samples collected from 17 Spanish subjects after a single oral dose of 25 mg losartan.

Results: The maximum plasma concentration of E-3174 was significantly (P < .05) lower in the CYP2C9*1/*3 (n = 5) and CYP2C9*2/*3 (n = 4) groups compared with the CYP2C9*1/*1 (n = 6) and CYP2C9*1/*2 (n = 3) groups and extremely low in 1 subject with the CYP2C9*3/*3 genotype. The ratio of the total losartan area under the plasma concentration–time curve (AUC) to the total E-3174 AUC (AUC_losartan/AUC_E-3174) was higher in the subject with the CYP2C9*3/*3 genotype (30-fold) and also in the CYP2C9*1/*3 and *2/*3 groups (approximately 2- and 3-fold, respectively) compared with the CYP2C9*1/*1 group. The plasma ratios correlated significantly with the 0- to 8-hour urinary losartan/E-3174 ratios. Among the total of 39 subjects, the urinary ratio was significantly higher in subjects with the CYP2C9*1/*3 (n = 10) and *2/*3 (n = 4) genotypes than in those with the CYP2C9*1/*1 genotype (n = 11; P < .01) and approximately 40-fold higher in subjects with the CYP2C9*3/*3 genotype (n = 3).

Conclusion: The CYP2C9*3 allele was shown to be associated with decreased formation of E-3174 from losartan. The significant differences between genotypes in plasma and urine losartan/E-3174 ratios and the good correlation between the plasma and urine ratios suggest that the losartan/E-3174 ratio in 0- to 8-hour urine specimens may serve as a phenotyping assay for CYP2C9 activity. Further studies in larger populations will be required to establish this.