What is pharmacogenetics and should we be using it?
Pharmacogenetics (PGx) is the science of understanding how a person’s genetics can influence drug treatment outcomes. Professor Graeme Suthers is one of Australia's most respected experts in the field of genetics. He explains that whilst PGx testing has demonstrated clear benefits and is standard practice in many other countries, it is still underrepresented in Australia and New Zealand.
“The term PGx was introduced in the 1960s when a team of researchers recognised that there was an interaction between genes and drugs. During a study, a series of adults were given a standard dose of Isoniazid, an anti TB medication, which was measured to ensure they all had the same concentration of the drug in their blood. When the concentration of Isoniazid was measured in each of the patients after a standard interval, they found that there wasn’t a smooth distribution across the group. Instead, the group was clearly split in two; those with a high concentration and those with a low concentration. This pointed to an underlying genetic factor which was binary i.e., the gene was either present or absent, and had influence on how the Isoniazid was absorbed and distributed.
“The concept there is a fundamental one – patients respond to medications differently because of variations in genes that determine medication exposure and response. For much of the last 60 years, the development of drugs, along with the choice and dose of drugs, has been run on the assumption that we are dealing with the average person. What PGx can potentially do is treat a patient as an individual and personalise drug choice and dose, rather than treating everyone as the average patient. By using PGx testing, a clinician can align a prescription with the patient’s potential for a beneficial or adverse response to a drug,” said Prof Suthers.
A report in 2008 estimated that the widespread implementation of PGx testing in Australia could yield savings in excess of $1 billion annually by the avoidance of adverse medication reactions alone. As PGx testing only needs to be performed once overall, it is unlike blood glucose or blood pressure monitoring where patients have to do repeated testing.
“It’s really only in the past 10-15 years that we have had sufficient genetic testing with a comparatively low cost and sufficient data about genes and drugs to make confident predictions. We are at the point now where it is well established in many parts of the world. In fact, having a gene test to work out how medication should be titrated or adjusted for an individual’s metabolism is standard of care in many parts of the world today.
We are certainly seeing more interest in PGx, and the tests are being used to inform prescribing among doctors. However, we are still quite far behind where our counterparts are in North America and Europe. There are opportunities for applications to the Medical Services Advisory Committee for funding of these tests on the Medical Benefits Schedule (MBS)
“The field has unfortunately been damaged by some over-hyping of PGx, particularly in some overseas centres, making claims that can’t be sustained. This has unfortunately led people to dismiss all claims about the potential values of PGx. It is important that we take a review of the evidence for the utility and apply PGx where there is clear evidence of benefits,” said Prof Suthers.
 Australian Centre for Health Research. Improving the quality use of medicines in Australia: Realising the potential of pharmacogenomics. Melbourne: ACHR, 2008