Pharmacogenomics: the future of drug therapy

Pharmacogenetics and pharmacogenomics of sexual dysfunction: current status, gaps and potential applications

Although treatment of different types of sexual dysfunction has improved in the past decade with the introduction of phosphodiesterase type 5 inhibitors and selective serotonin reuptake inhibitors, response rates to these targeted therapies are variable. There are a number of studies in the published literature that provide proof-of-concept that genetic variation contributes to the variable response. Pharmacogenomics will most likely be one part of our therapeutic armamentarium in the future and will provide a stronger scientific basis for optimizing drug therapy on the basis of each patient’s genetic constitution. This article will review English language medical literature on the state-of-the-art genetic polymorphisms of drug targets, transporters and signaling molecules as well as pharmacogenetic studies of sexual dysfunction and suggested possible applications. Collectively, the data demonstrate that pharmacogenomics in the field of sexual medicine is still in its infancy. More research will provide further intriguing new discoveries in years to come.

Human pharmacogenomic variations and their implications for antifungal efficacy

Pharmacogenomics is defined as the study of the impacts of heritable traits on pharmacology and toxicology. Candidate genes with potential pharmacogenomic importance include drug transporters involved in absorption and excretion, phase I enzymes (e.g., cytochrome P450-dependent mixed-function oxidases) and phase II enzymes (e.g., glucuronosyltransferases) contributing to metabolism, and those molecules (e.g., albumin, A1-acid glycoprotein, and lipoproteins) involved in the distribution of antifungal compounds. By using the tools of population genetics to define interindividual differences in drug absorption, distribution, metabolism, and excretion, pharmacogenomic models for genetic variations in antifungal pharmacokinetics can be derived. Pharmacogenomic factors may become especially important in the treatment of immunocompromised patients or those with persistent or refractory mycoses that cannot be explained by elevated MICs and where rational dosage optimization of the antifungal agent may be particularly critical. Pharmacogenomics has the potential to shift the paradigm of therapy and to improve the selection of antifungal compounds and adjustment of dosage based upon individual variations in drug absorption, metabolism, and excretion.

Preparation of poly(ethylene glycol)-introduced cationized gelatin as a non-viral gene carrier

The objective of this study was to prepare cationized gelatins grafted with poly(ethylene glycol) (PEG) (PEG-cationized gelatin) and evaluate the in vivo efficiency as a non-viral gene carrier. Cationized gelatin was prepared by chemical introduction of ethylenediamine to the carboxyl groups of gelatin. PEG with one terminal of active ester group was coupled to the amino groups of cationized gelatin to prepare PEG-cationized gelatins. Electrophoretic experiments revealed that the PEG-cationized gelatin with low PEGylation degrees was complexed with a plasmid DNA of luciferase, in remarked contrast to that with high PEGylation degrees. When the plasmid DNA complexed with the cationized gelatin or PEG-cationized gelatin was mixed with deoxyribonuclease I (DNase I) in solution to evaluate the resistance to enzymatic degradation, stronger protection effect of the PEG-cationized gelatin was observed than that of the cationized gelatin. The complex of plasmid DNA and PEG-cationized gelatin had an apparent molecular size of about 300 nm and almost zero surface charge. These findings indicate that the PEG-cationized gelatin-plasmid DNA complex has a nano-order structure where the plasmid DNA is covered with PEG molecules. When the PEG-cationized gelatin-plasmid DNA complex was intramuscularly injected, the level of gene expression was significantly increased compared with the injection of plasmid DNA solution. It is concluded that the PEG-cationized gelatin was a promising non-viral gene carrier to enhance gene expression in vivo.

Improving pharmacotherapy outcomes by pharmacogenomics: from expectation to reality?

The genomic era is now a reality and the extraction of genomic information with a practical value in healthcare represents the next challenge following the completion of the Human Genome Project. To this end, the first pharmacogenomics test approved by the US Food & Drug Administration for assessing cytochrome P450 (CYP)2D6 and CYP2C19 genotype in the implementation of pharmacotherapy decisions in patients, is expected to improve pharmaceutical care outcomes, at least for drugs that are substrates or inhibitors of these enzymes. Furthermore, the progress already achieved and the experience gained in the fields of pharmacogenomics and personalized medicine has clearly demonstrated that an interdisciplinary approach could better serve the target of improving pharmacotherapy outcomes in routine clinical practice. Such an approach will obviously move drug prescription towards pharmacotyping, a stage where the drug selection and dosage process carried out by medical practitioners for any given patient will be advanced by genomic knowledge and information.

Does pharmacogenomics provide an ethical challenge to the utilisation of cost-effectiveness analysis by public health systems?

Pharmacogenomics promotes an understanding of the genetic basis for differences in efficacy or toxicity of drugs in different individuals. Implementation of the outcomes of pharmacogenomic research into clinical practice presents a number of difficulties for healthcare. This paper aims to highlight one of the unique ethical challenges which pharmacogenomics presents for the utilisation of cost-effectiveness analysis by public health systems. This paper contends that pharmacogenomics provides a challenge to fundamental principles which underlie most systems for deciding which drugs should be publicly subsidised. Pharmacogenomics brings into focus the conflict between equality and utility in the context of using cost-effectiveness analysis to aid distribution of a limited national drug budget.

The Epidemiologic Approach to Pharmacogenomics

The epidemiologic approach enables the systematic evaluation of potential improvements in the safety and efficacy of drug treatment which might result from targeting treatment on the basis of genomic information. The main epidemiologic designs are the randomized control trial, the cohort study, and the case-control study, and derivatives of these proposed for investigating gene-environment interactions. However, no one design is ideal for every situation, and methodological issues, notably selection bias, information bias, confounding and chance, all play a part in determining which study design is best for a given situation. There is also a need to employ a range of different designs to establish a portfolio of evidence about specific gene-drug interactions. In view of the complexity of gene-drug interactions, pooling of data across studies is likely to be needed in order to have adequate statistical power to test hypotheses. We suggest that there may be opportunities (i) to exploit samples from trials already completed to investigate possible gene-drug interactions; (ii) to consider the use of the case-only design nested within randomized controlled trials as a possible means of reducing genotyping costs when dichotomous outcomes are being investigated; and (iii) to make use of population-based disease registries that can be linked with tissue samples, treatment information and death records, to investigate gene-treatment interactions in survival.

The role of cost-effectiveness analysis in the era of pharmacogenomics

The broad availability of genetic information and technologies heralds an era when practitioners will utilise genomic testing to individualise patients' care. Pharmacogenomics uses a spectrum of approaches to explore the association of genetic variation with drug efficacy or toxicity. Investigators have described a broad array of genetic polymorphisms that confer inter-individual differences in drug response. Pharmacogenomics offers the potential to improve drug effectiveness, reduce adverse drug reactions and provide cost-effective care. However, it has had little impact on current clinical practice and the economic implications of pharmacogenomics remain unclear. Assessing the incremental cost effectiveness of a pharmacogenomic strategy involves examination of factors associated with the genotype of interest, the genomic test, the disease state and the treatment. A pharmacogenomic strategy is likely to be cost effective when: (i) the polymorphism under consideration is prevalent in the population and has a high degree of penetrance; (ii) genetic testing is highly sensitive and specific, and less costly alternative tests that could be used to individualise therapy are not readily available; (iii) the disease state involves outcomes with significant morbidity or mortality if left untreated; and (iv) the treatment involves significant outcomes and/or costs that can be impacted by genotype-individualised therapy. We foresee pharmacogenomic applications being particularly relevant for drugs: with a narrow therapeutic index or a high degree of variability in inter-individual response; where there are limitations in current methods for monitoring their adverse effects and treatment responses; and where there are few alternative treatment options. Because of the characteristics of chemotherapeutic agents and the severity of clinical outcomes in cancer, oncology appears to be one of the most appropriate disease areas for the application of pharmacogenomics. We have developed a framework which can assist researchers, pharmacists, physicians, and policy makers in evaluating the implications of specific strategies, and identifying when formal cost-effectiveness analyses should be conducted to quantitatively evaluate the benefits of pharmacogenomics.

Protecting communities in pharmacogenetic and pharmacogenomic research

The existing EELS literature has usefully identified the scope of ethical issues posed by pharmacogenetic and pharmacogenomic research. The time has come for in-depth examination of particular ethical issues. The involvement of racial and ethnic communities in pharmacogenetic and pharmacogenomic research is contentious precisely because it touches upon the science and politics of studying racial and ethnic difference. To date, the ethics literature has not seriously taken account of the fact that such research impinges upon the interests of communities, and that taking such interests seriously requires that we both protect and empower communities in research. We propose a framework that rests upon the recognition that communities are heterogeneous human associations and differing policies are appropriate for differing communities. Community consent and consultation and community consultation alone are neither appropriate nor required for all pharmacogenetic and pharmacogenomic research. Rather, application of these policy protections must take into account particulars of both planned research and the communities involved.