The Response Of Pharmacogenetics
In the present time of clinical use of a drug
, the physician does not have any means of foretelling the reactions of a patient to a prescribed medicine. Unchangeably, there are patients who do not manifest positive response, and patients who show Adverse Drug Reactions. Thus, the task of prescribing drugs is relatively an empirical trial and error, which often results to changing the choice of drugs and or its dose.
Because most of the ADRs are type A pharmacological reactions-A for augmentation and which results from raised plasma concentrations-they should be preventable and predictable. This is a very favorable goal because a number of studies have a constant result showing that ADRs and their management compose a significant encumbrance on healthcare resources.
The surprising reactions to drugs often result from a 'standard' dose schedules that are typically recommended, disregarding the divergent inter-individual differences within the patient population. Up to the present, the drugs are developed, approved and marketed on a 'one size fits all' basis from sub-population-based mean data on effectiveness, safety and dose.
There is a general presumption that every patient belongs to a homogenous group manifesting little or no inter-individual differences. This is manifested from drug development program that customarily tends to reduce or remove, instead of embracing, differences in the populations that are randomized into clinical trials and aimed on a very limited dose range.
The factors of pharmacogenetic function at pharmacokinetic and pharmacodynamic level-two key compositions of the dose-response curve of a medicine. The dose-response relationship between individuals is influenced by pharmacological targets of drugs and the polymorphisms in drug metabolizing enzymes.
For certain drugs, while the retrospective information from case studies indicates that polymorphisms are linked to adverse drug reactions or inefficacy, the clinical utility of this information remains to be unproven.
Hence, there is an urgent need for prospective data to ascertain whether pre-treatment genotyping can enhance treatment. The varying guidelines for regulation have already recommended exploration of the role of genetic factors in examining a drug for its pharmacokinetics, pharmacodynamics, dose-response relationship and the potential of drug intervention.
Emerging from the worldwide heterogeneity in the frequency of variant alleles, the regulatory guidelines likewise demand the sponsors to produce more information-such as pharmacogenetic bridging data-to ascertain whether the data from one ethnic population can be conjectured to another.
Meanwhile, in the current situation, the sponsors examine the pharmacogenetic impact in early clinical pharmacokinetic studies. However, it is very rare that they carry the diagnosis forward when designing dose-response studies.
Having a greater incorporation of pharmacogenetics in developing drug, the regulatory authorities should expect more detailed genetic data. In turn, this will result to complicating the process of drug evaluation, and the consequences of complex prescribing information.
Moreover, not all differences in drug responses are linked to pharmacogenetic polymorphisms. The drug response can be regulated by a few non-genetic factors including co-medications and the presence of concurrent illnesses.
On the other hand, pharmacogenetic will have a better future in clinical practice should there be discovered a highly predictive genotype-phenotype relationships during development of drug and demonstrating their clinical validity and utility in prospective clinical trials.
by: Charles Godbout
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