The effect of the CYP2C19*2 heterozygote genotype on the pharmacokinetics of nelfinavir

Functional genetic polymorphisms in CYP2C19 gene in relation to cardiac side effects and treatment dose in a methadone maintenance cohort

Abstract Methadone maintenance therapy is an established treatment for heroin dependence. This study tested the influence of functional genetic polymorphisms in CYP2C19 gene encoding a CYP450 enzyme that contributes to methadone metabolism on treatment dose, plasma concentration, and side effects of methadone. Two single nucleotide polymorphisms (SNPs), rs4986893 (exon 4) and rs4244285 (exon 5), were selected and genotyped in 366 patients receiving methadone maintenance therapy in Taiwan. The steady-state plasma concentrations of both methadone and its EDDP metabolite enantiomers were measured. SNP rs4244285 allele was significantly associated with the corrected QT interval (QTc) change in the electrocardiogram (p=0.021), and the Treatment Emergent Symptom Scale (TESS) total score (p=0.021) in patients who continued using heroin, as demonstrated with a positive urine opiate test. Using the gene dose (GD) models where the CYP2C19 SNPs were clustered into poor (0 GD) versus intermediate (1 GD) and extensive (2 GD) metabolizers, we found that the extensive metabolizers required a higher dose of methadone (p=0.035), and showed a lower plasma R-methadone/methadone dose ratio (p=0.007) in urine opiate test negative patients, as well as a greater QTc change (p=0.008) and higher total scores of TESS (p=0.018) in urine opiate test positive patients, than poor metabolizers. These results in a large study sample from Taiwan suggest that the gene dose of CYP2C19 may potentially serve as an indicator for the plasma R-methadone/methadone dose ratio and cardiac side effect in patients receiving methadone maintenance therapy. Further studies of pharmacogenetic variation in methadone pharmacokinetics and pharmacodynamics are warranted in different world populations.

CYP2C19 genetic variants affect nelfinavir pharmacokinetics and virologic response in HIV-1-infected children receiving highly active antiretroviral therapy

BACKGROUND

The objective of this research was to identify the impact of genetic variants of P-glycoprotein (ABCB1) and cytochrome P450 (CYP) on nelfinavir pharmacokinetics and response to highly active antiretroviral therapy (HAART) in HIV-1-infected children.

METHODS

HIV-1-infected children (n = 152) from Pediatric AIDS Clinical Trial Group 366 or 377 receiving nelfinavir as a component of HAART were evaluated. Genomic DNA was assayed for ABCB1 and CYP genetic variants using real-time polymerase chain reaction Nelfinavir oral clearance (CL/F), M8 to nelfinavir ratios, CD4 T cells, and HIV-1-RNA were measured during HAART.

RESULTS

Nelfinavir CL/F and M8 to nelfinavir ratios were significantly associated with the CYP2C19-G681A genotypes (P < 0.001). Furthermore, the CYP2C19-G681A genotype was related to virologic responses at week 24 (P = 0.01). A multivariate analysis demonstrated that age (P = 0.03), concomitant protease inhibitor use (P < 0.001), and the CYP2C19-G681A genotype (P < 0.001) remained significant covariates associated with nelfinavir CL/F.

CONCLUSIONS

CYP2C19 genotypes altered nelfinavir pharmacokinetics and the virologic response to HAART in HIV-1-infected children. These findings suggest that CYP2C19 genotypes are important determinants of nelfinavir pharmacokinetics and virologic response in HIV-1-infected children.

Influence of CYP2C19 polymorphism on the pharmacokinetics of nelfinavir and its active metabolite

AIMS

This study reports the pharmacokinetics of nelfinavir, its active metabolite, M8, and active moiety (nelfinavir + M8) in volunteers genotyped for CYP2C19 as extensive metabolizer (*1*1; n = 38), heterozygous poor metabolizer (PM) (*1*2; n = 22) and homozygous PM (*2*2; n = 6).

METHODS

Subjects received nelfinavir at normal dose (3.5 days of 1250 mg q12h) or high dose (1250 mg q12h for 3 days and single dose of 3125 mg on day 4). Steady-state plasma samples were analysed by high-performance liquid chromatography/ultraviolet assay to determine pharmacokinetics.

RESULTS

At steady state, the mean C(max) was 42% [95% confidence interval (CI) 19, 69] and 63% (95% CI 20, 122) higher, and mean AUC was 51% (95% CI 24, 83) and 85% (95% CI 32, 159) higher for *1*2 and *2*2 compared with *1*1 subjects, respectively. For M8, the mean C(max) and AUC were 35% (95% CI 6, 55) and 33% (95% CI -3, 56), respectively, lower for *1*2 compared with *1*1 subjects. M8 was not detectable in *2*2 subjects. The mean C(max) and AUC values for the active moiety were higher by 30-35% for the *1*2 and *2*2 compared with *1*1 subjects.

CONCLUSIONS

Mutation in CYP2C19 increased the systemic exposure of nelfinavir and reduced the exposure of M8. No significant differences were noted among the heterozygous (*1*2) and homozygous (*2*2) PMs. These changes are not considered to be clinically relevant and hence the use of nelfinavir does not require prior assessment of CYP2C19 genotype.

The impact of pharmacogenetics on HIV therapy

Summary

The use of highly active antiretroviral therapy in the treatment of HIV infection has resulted in significant reductions in mortality and morbidity worldwide. However, there is considerable interindividual variability in patient outcomes in terms of drug disposition, drug efficacy and adverse events. The basis of these differences is multifactorial, but host genetics are believed to play a significant part. To date, most attempts to explain this variability have focused on isolated single nucleotide polymorphisms. The most exciting development to date is the discovery of human leukocyte antigen subtype B*5701 (HLA B*5701) as a strong predictor of the abacavir hypersensitivity reaction. There is a gradual move away from single candidate gene analyses towards a high throughput whole genome approach. These studies must be performed on well characterized cohorts and reported associations must be validated in independent, ethnically diverse populations.

Advances in pharmacogenomics of antiretrovirals: an update

Recent developments in the pharmacogenomics of antiretroviral drugs provide new prospects for predicting the efficacy of treatment and potential adverse effects. HIV/AIDS is a serious but treatable infectious disease, yet current treatment is limited by high rates of adverse drug reactions and development of resistance due to suboptimal drug concentrations in a significant proportion of patients. Antiretroviral therapy is especially suitable for pharmacogenomic investigation as both drug exposure and treatment response can be quantified and certain adverse effects can be assessed with validated measures. Additionally, there is increasing knowledge of the pharmacokinetics and dynamics of antiretroviral drugs, and some candidate genes implicated in the metabolism, transport and adverse effects have been identified. However, recent studies of the association of particular genes and their genetic variants with HIV management and adverse drug reactions have not provided unifying conclusions. This article reviews the most recently published work and summarizes the state of research in this area. Future directions for research and the application of this technology to the clinical practice of individualizing treatment for HIV management are discussed.

Pharmacogenetics and the potential for the individualization of antiretroviral therapy

PURPOSE OF REVIEW

Genetic associations highlighting differences in the response to HIV infection and treatment have significantly furthered our understanding of the pathogenesis, pharmacokinetics and pharmacodynamics of antiretroviral drug action and toxicities and HIV disease itself. This review focuses on the current knowledge of associations between polymorphisms and treatment outcomes in HIV with particular emphasis on clinically relevant relationships likely to lead to the individualization of antiretroviral therapy.

RECENT FINDINGS

Our understanding of the immunogenetic basis of drug toxicity has been furthered by human leucocyte antigen associations with hypersensitivities for the antiretroviral drugs abacavir and nevirapine. For abacavir in particular, the use of HLA-B*5701 as a screening test appears to be generalizable across racially diverse populations and has been supported by both observational, and blinded randomized controlled trials.

SUMMARY

Differences in HIV acquisition and progression as well as antiretroviral efficacy and toxicity will continue to provide the basis for research to define the genetic basis of such diversity. Despite the plethora of research in this area, numerous barriers exist to the successful operationalization of genetic testing to the clinic. HLA-B*5701 screening to prevent abacavir hypersensitivity is currently the most relevant to clinical practice and highlights that the promise of cost-effective testing can be facilitated by robust laboratory methodology and quality assurance programs that can be applied to diverse treatment settings.

Pharmacogenetics of Anti-HIV Drugs

Pharmacogenetics holds promise in HIV treatment because of the complexity and potential toxicity of multidrug therapies that are prescribed for long periods. Thus far, few candidate genes have been examined for a limited number of allelic variants, but a number of confirmed associations have already emerged. A change in paradigm emerges from the availability of the HapMap, the wealth of data on less-common genetic polymorphisms, and new genotyping technology. This review presents a comprehensive analysis of the existing literature on pharmacogenetic determinants of antiretroviral drug exposure, drug toxicity, as well as genetic markers associated with the rate of disease progression. It is expected that larger-scale comprehensive genome approaches will profoundly change the landscape of knowledge in the future.

Effect of CYP2C19 polymorphism on nelfinavir to M8 biotransformation in HIV patients

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

* Nelfinavir is an HIV protease inhibitor, substrate of the transporter P-glycoprotein and metabolized via CYP2C19, CYP3A4 and CYP3A5 enzymes. * Pharmacokinetic studies have shown wide interindividual variability of nelfinavir concentrations, some of this variability perhaps caused by variant drug metabolism or transporter genes. * For CYP3A4*1B and CYP3A5*3 polymorphism, results from three studies are in agreement, showing no difference in nelfinavir concentrations between patients with these different genotypes. * However, for MDR1 and CYP2C19 polymorphism, there have been contradictory studies, showing either no impact on nelfinavir concentration or modified concentrations which could influence virological response.

WHAT THIS STUDY ADDS

* Patients with an *1/*2 or *2/*2 genotype for CYP2C19 had a nelfinavir to M8 biotransformation divided by 2 compared with *1/*1 patients. * No evidence of any influence of MDR1 polymorphism on nelfinavir absorption could be detected.

AIMS

To evaluate the effect of CYP2C19 polymorphism on nelfinavir and M8 pharmacokinetic variability in human immunodeficiency virus-infected patients and to study the link between pharmacokinetic exposure and short-term efficacy and toxicity.

METHODS

Nelfinavir (n = 120) and M8 (n = 119) concentrations were measured in 34 protease inhibitor-naive patients. Two weeks after initiating the treatment, blood samples were taken before, 1, 3 and 6 h after drug administration. Genotyping for CYP3A4, 3A5, 2C19 and MDR1 was performed. A population pharmacokinetic model was developed to describe nelfinavir-M8 concentration time-courses and to estimate interpatient variability. The influence of individual characteristics and genotypes were tested using a likelihood ratio test. Estimated mean (C(mean)), maximal (C(max)) and trough (C(trough)) nelfinavir and M8 concentrations were correlated to short-term virological efficacy and tolerance using Spearman nonparametric correlation tests.

RESULTS

A one-compartment model with first-order absorption, elimination and metabolism to M8 best described nelfinavir data. M8 was modelled by an additional compartment. Mean pharmacokinetic estimates and the corresponding intersubject variabilities were: absorption rate 0.17 h(-1) (99%), absorption lag time 0.82 h, apparent nelfinavir total clearance 52 l h(-1) (49%), apparent nelfinavir volume of distribution 191 l, M8 elimination rate constant 1.76 h(-1) and nelfinavir to M8 0.39 h(-1) (59%) in *1/*1 patients and 0.20 h(-1) in *1/*2 or *2/*2 patients for CYP2C19*2. Nelfinavir C(mean) was positively correlated to glycaemia and triglyceride increases (P = 0.02 and P = 0.04, respectively).

CONCLUSIONS

The rate of metabolism of nelfinavir to M8 was reduced by 50% in patients with *1/*2 or *2/*2 genotype for CYP2C19 compared with those with *1/*1 genotype.

Pharmacogenetic Considerations in the Management of HIV Infection

Potent combination antiretroviral drug therapy has now been available to HIV-infected patients for more than a decade, resulting in a significant decline in disease-related morbidity and mortality. Nonetheless, a number of HIV-infected individuals fail to experience the full benefit of their antiretroviral medications; some lack a robust virologic response, while others experience treatment-limiting toxicities. A number of factors may contribute to variable drug response in patients with HIV infection. Virologic, immunologic, pharmacologic, and pharmacokinetic differences between HIV-infected patients have all been noted to contribute to interpatient variability in drug response. Recent data suggest that pharmacogenetic differences among HIV-infected individuals may also be an important variable that contributes to antiretroviral drug response. Pharmacogenetic studies of antiretroviral drug therapy have explored the influence of single nucleotide polymorphisms in genes responsible for key proteins involved in antiretroviral drug metabolism (cytochrome P50 enzymes) and drug transport (P-glycoprotein). In addition, the human leukocyte antigen genotype (HLA-B*57) has been found to predict abacavir-associated hypersensitivity reactions. Antiretroviral pharmacogenetics offers the possibility of optimizing virologic response and minimizing drug toxicity by individualizing anti-HIV pharmacotherapy. The authors review those genetic polymorphisms that have been shown, or are strongly suspected, to influence antiretroviral drug metabolism, transport, and toxicity.