Estimation of plasma levels of warfarin and 7-hydroxy warfarin by high performance liquid chromatography in patients receiving warfarin therapy.

Warfarin is one of the most commonly prescribed oral anticoagulant for prevention of thromboembolic events. The effect of this drug is measured by monitoring prothrombin time expressed as International Normalized Ratio (INR). In some cases, however, the measurement of plasma concentration of warfarin was emphasized. In the present study, reversed phase high performance liquid chromatography (HPLC) was used to estimate the plasma drug levels. A total of 185 patients were enrolled in this study. Five milliliter of venous blood was collected using sodium EDTA tubes for pharmacokinetic analysis. Solid phase extraction was used to recover the warfarin and it's metabolite from plasma using isopropanol and potassium phosphate buffer (40:60) mobile phase. Warfarin, 7-hydroxy warfarin and carbamazepine (internal standard) were separated on a C18 column and had the retention time 3.6 min, 2.9 min and 5.9 min, respectively. The assay was linear in warfarin concentration ranges of 0.1-5 µg/ml. The extraction recovery was found to be ≃85%. The mean plasma concentrations of warfarin and 7-hydroxy warfarin were found to be 3.47 ± 1.87 (SD) µg/ml, 1.25 ± 0.81 (SD) µg/ml, respectively. Through the present study the plasma concentrations of warfarin, 7-hydroxy warfarin and their metabolic ratio was determined. The assay was sensitive to follow warfarin pharmacokinetics in a patient with warfarin therapy for 3 months and above.

Genetic variations and haplotypes of the 5' regulatory region of CYP2C19 in South Indian population.

CYP2C19 is expressed polymorphically with about 21 variant alleles. Genotype-phenotype association studies of CYP2C19 have shown marked deviations, suggesting the presence of other variations in the intronic and 5' regulatory region affecting its expression. This study aims to identify the genetic polymorphisms and construction of haplotypes of variations in 5' regulatory region of CYP2C19 among the South Indian population. CYP2C19 5' regulatory region was amplified and sequenced from the DNA of 58 healthy volunteers of South Indian origin. Genetic analysis revealed the existence of 14 variations including eight novel ones in the 5' regulatory region. Identified novel variations and their percentage frequencies were: -779A>C (16.4), -828T>A (2.6), -934del>T (3.5), -1051T>C (1.72), -1289T>G (3.4), -1442T>C (12.1), -1498T>G (25.0) and -1558T>G (2.6). The reported variations found in the study population and their frequencies were: -98T>C (28.4), -806C>T (2.6), -833del>T (9.5), 889T>G (10.3), -1041A>G (100.0) and -1418C>T (1.7). The two known non synonymous single nucleotide polymorphisms, 681G>A ((*)2 allele) and 636G>A ((*)3 allele) were detected at 0.371 and 0.025 frequencies, respectively. Forty three haplotypes were constructed and linkage disequilibrium analysis showed strong linkage between several variations identified in the gene. Fourteen polymorphisms including 8 novel ones in CYP2C19 5' flanking region are reported for the first time in an Indian population from South India. Results from this study provide additional information for genotyping of CYP2C19 in the South Indian population and probably in the Indian population.

Influence of the genetic polymorphisms in the 5' flanking and exonic regions of CYP2C19 on proguanil oxidation.

CYP2C19 is a polymorphic enzyme which metabolizes several clinically important drugs including proguanil. Variation in the 5' regulatory region may influence CYP2C19 activity. This study evaluates the relationship between proguanil metabolic ratio and genetic variations of CYP2C19 in a South Indian population. Fifty unrelated healthy subjects were genotyped for CYP2C19 (*)2 and (*)3 alleles and the 5' flanking region of CYP2C19 was sequenced. Plasma concentrations of proguanil and cycloguanil were estimated by reverse phase HPLC after single oral doses (200 mg) of proguanil. In silico docking analysis of transcription factors binding to its sites in CYP2C19 5' regulatory region was performed. The mean metabolic ratios (proguanil/cycloguanil) were highest in (*)1/(*)2 or (*)1/(*)3 subjects and in (*)2/(*)2 or (*)2/(*)3 as compared to (*)1/(*)1 subjects. Subjects with promoter region variation -98T>C showed decrease in the metabolic ratios irrespective of other variation, which may explain the deviation from the genotype-phenotype association of CYP2C19. In silico analysis predicted alteration in the interaction of transcription factors to their binding sites in the presence of variant alleles. The results of this study would be useful in predicting interindividual differences in the metabolism of substrates of CYP2C19.