8 August 2012

Matching medication to a patient’s genetic

By Dr Hwang Siaw San

Imagine this: you’re at the doctor’s office after coming down with a fever. Before he prescribes your medication, he conducts a genetic test to predict how you would respond to a drug.  

While this may sound like a scene out of a science fiction film such a test is now possible in pharmacogenomics, a study of genes that determines a person’s response to a drug, including drug metabolism.  Knowledge on these variations can be used to predict whether a patient will have a good or bad response to a drug or negligible response at all.

An emerging field and a term derived from the words “pharmacology” and “genomics”, pharmacogenomics also helps to explain why we require varying doses of a drug to achieve an optimal therapeutic outcome.

Such information allows medication to be personalised, where clinical, genetic and molecular information is used to optimize treatment and health outcomes for an individual.

Pharmacogenomics gained attention following observations that not everyone respond the same way to the same drugs. Apart from age, lifestyle and overall health, reactions to medications are also influenced by genetic profile, especially the variability of the gene expressions between people in their responses to drugs. This means that although one type of drug may work for you, it might not work for others. Researchers are now working to match specific gene variations with responses to specific medications.   

The discovery of the small changes in the nucleotide or DNA base of one’s genes has made the genetic test for predicting drug responses possible. These differences might give us implication on the efficacy of drug used and also how well our enzymes metabolize the drugs. Genetic markers known as single-nucleotide polymorphisms or SNPs (pronounced “snips”) have been applied in pharmacogenomics and personalized medicines for a wide range of diseases.  SNPs are DNA sequence variations that occur when a single base adenine (A), thymine (T), cytosine (C), or guanine (G) in the genome sequence is changed.  The presence of SNPs can be determined by the DNA sequencing technique, and can be used as diagnostic tools to predict an individual’s drug response.  SNPs found in genes for drug metabolizing enzymes might influence the ability of an individual to process the drug effectively. 

Currently, pharmacogenomics is applied to determine drug responses in the treatment of cardiac, respiratory and psychiatric conditions. It is also applied in the development of drugs for the treatment of dementia, cancer and cardiac conditions.

Pharmacogenomics testing allows for the rapid identification of patients who are not responding well to a particular drug or patients who will respond well to a particular drug.  The information gained from such tests can be utilised to optimize treatment by selecting the most efficient drugs along with the appropriate doses. 

Some of the potential benefits of pharmacogenomics include the development of drugs with better therapeutic effects that targets specific health problems and prescription of drugs based on an individual’s genetic profile with minimized adverse reactions. 

However, there are limitations in pharmacogenomics. Targeting different drugs can be very complex, mainly because many genes are involved in the way an individual responds to a drug.  Other factors such as age, sex, body weight, nutrient level, infections and lifestyle may contribute to the variations in one’s responses as well.  The identification of an individual’s gene variation that may be involved in drug metabolism is also time-consuming. In addition, due to the high costs involved in SNP analysis and genotyping test, health insurance companies may refuse to pay for extra diagnostic tests.

Genotype tests before drug therapy is not only a promising approach to reduce the effects of inter-individual variation in drug responses. It also enhances the efficiency of drug delivery.  Besides, an understanding of the genetic variability in drug responses also helps pharmaceutical companies to design more effective new therapies. 

Perhaps one day drugs which adapts to the genetic makeup of a patient, and thus with higher efficacy, may be tailor-made. However, professional guidelines and expertise are still needed in the evaluation and interpretation of test results in order to provide good clinical recommendations on individualized medications. In addition, regulations on prescription guidelines, testing and usage labels will be needed if pharmacogenomics testing is to be widely used.

Dr Hwang Siaw San is a lecturer with the School of Engineering, Computing and Science at Swinburne University of Technology Sarawak Campus. She is contactable at shwang@swinburne.edu.my