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Personalized Medicine Coalition was formed in 2005 to represent researchers, scientists, innovators, and healthcare professionals to encourage the inclination of understanding the concept of personalized medicines particularly in the stream of medicines to follow for the betterment of patient healthcare system. They define personalized medicines as the combination treatment of the results obtained from the diagnosis and the application of the patients’ genomic data to opt a medicine and to design a suitable facilitated delivery system at the right time to the target site knowing the predisposition condition of that disease in individual patients [15]. Personalized medicines make the practitioner to establish in-depth knowledge at the molecular level to understand the disease condition and increase the treatment outcomes to its best at the earliest. It is an advanced trend in the field of health involving the patient’s genetic data, medical and medication history, and habitat. A schematic flow of personalized/customized medicine is represented in Figure 3.1 [16]. The ultimate aim of personalized medicines is to serve the patients’ wants and treatment needs by reducing the adverse effects increasing the therapeutic action. For the effective implementation of personalize medicine the collective approach of adopting pharmacogenomics as a diagnostic tool and nanotechnology as a drug delivery tool servers added advantage to patients [17].

In the initial 21^st century, Brian B&Spear gives an opinion on the clinical applications of pharmacogenetics in personalized medicines. It is well understood that appropriate safety and efficacy of drug candidates are mandatory for approval. This act of ascertaining is based on the statistical approach among the unhealthy human population. It concludes that the drug candidate is not effective or safe for every individual patient; the inherent interindividual variations among the patients significantly influence the quality, efficacy, and safety of the patient health. A case study was conducted categorizing various therapeutic areas with that of its percentage efficacy in published data summarized in Figure 3.2. The lowest percentage of responsive patients is 25% for oncology and 85% is for analgesic (COX-2 inhibitors) agents. Most of the therapeutic agents are responsive to 50% to 75% of the population only. In those few are non-responders showing no benefits, and few continue to suffer the disease symptoms. The drug safety also differs from one drug substance to another and from disease to disease, though most of the drugs exhibit secondary effects and adverse effects as important clinical indications, despite the intensified several attempts of the pharmaceutical industries in developing a safe drug moiety and the efforts of regulatory bodies to hold rigid safety profile guidelines [18].

Based on the given case study on the need for a genetic and molecular level of differentiation among the patient population, it is essential for the healthcare professionals to titer the doses of the drugs for individual patients using the following technologies for safe and effective therapy [19].

Figure 3.1 Basic personalized drug delivery approach.

Figure 3.2 Response rates of patients to a major drug for a selected group of therapeutic areas.

The primary objective of a personalized and customized drug delivery system is to analyze the clinical pharmacogenetics of each and every individual to distinguish the responders and nonresponders in the patient population for a particular drug and also the differences in risks of adverse drug reactions among the same population with the same drug [20]. This information provides the best choice of drug for a particular individual or a group of patients for better therapy with lesser adverse drug reactions and maximum likeliness of efficacy. It is essential to test a patient to identify whether the individual is responsive or nonresponsive to the particular agent or a class of therapeutic agents. Similarly, it paves an opportunity to understand whether the individual is prone to adverse effects and its degree of risk/benefits [21].

A patient may or may not show therapeutic response to a particular drug or even its adverse effects. There exist many reasons such as drug–drug interactions, drug causing hypersensitive reactions, allergic reactions, wrong dosing, and medicament fault. On the other hand, the patient’s genetic susceptibility to pathogen remains ambiguous for the drugs’ inappropriate response. Various genes are shown to associate to a specific drug molecule showing no response or fluctuations in the therapeutic effects, and some may also lead to ADRs (adverse drug reactions) [22]. For example, 5-lipoxygenease (ALOX-5) directly influences the production of leukotrienes, helps in treating asthma; clinically it is proved that patients with gene expression of inactive alleles of 5-lipogenase are not responsive to ALOX-5 inhibitor. Likely drug metabolizing enzyme CYP2D6 having two non-expressive alleles cannot perform its functional metabolism of codeine to morphine and no activity of analgesia is showcased [23].

In 2017, Arellano et al. conducted a study on multiple ADRs associated with genetic polymorphism. CYP2D6 is a polymorphic isozyme having more than 100 allelic variants; it is suspected to have a higher degree of risk causing ADR in individuals using the commonly prescribed therapeutic agents such as analgesics, beta adrenergic antagonists, anti-arrhythmic, antipsychotics, antidepressants, and cough suppressants that are metabolized to an extent of 25% by CYP2D6 due to a higher dose of drug accumulation in systemic circulation. Likewise, the lack of this enzyme leads to poor effect of drug response in prodrugs like tramadol [24].

The study of the genetic relations associated with ADRs is more important; therefore, recognizing the pathophysiologic mechanism of the drug reactions helps to identify safer drugs and biomarkers in the future for prevention, diagnosis, and treatment of patients developing ADRs. Studies associated with genetics in relation to ADR are quite challenging due to their heterogeneity in clinical demonstrations and broad range of therapeutic agents causing ADRs [25]. From the above-discussed examples and the needs of the patients for better therapy, the transformation of pharmacogenomics and pharmacogenetics in the field of advancing medicines must be enhanced by creating a patient genetic database, providing the healthcare professionals with detailed information about the predisposition of the therapy for a particular disease and drug [26]. The nongenomic factors acculturate a significant and better composition of data to increase the exactness of the patient therapy, which includes clinical and environmental factors. The advancing field of pharmacogenomics is now highly attractive and is now newly encouraged by the poly-omics tech. A gathered determination is necessary for the healthcare professionals to equip the implications of pharmacogenomic technique essentially and fundamental research in the area of clinical healthcare community, commercial enterprises, and regulatory bodies [27].