Pharmacogenetics (PGx) is the analysis of genes involved in the way a medication is handled by a person’s body, and the impact that the medication will have on that person. There is growing evidence that such tests are useful, allowing for more personalised prescribing. This reduces the patient’s chance of an adverse reaction to the medication.

However, there is a significant practical barrier: if the test is requested when the doctor is about to prescribe a medication, it can take 1-2 weeks to get the result, thereby delaying the prescribing decision. One way of addressing this barrier would be to test patients before any prescribing decision is being considered so that the result is available whenever it might be required in the future. This is called pre-emptive PGx testing and has not been rigorously tested.

PREPARE Trial

Earlier this year, a landmark study on the usefulness of pre-emptive PGx in Europe was published. This study was designed to assess whether knowing a patient’s PGx result reduced the chance of the patient having an adverse reaction to a medication prescribed by the doctor. The study, called the Pharmacogenomic Testing for Preventing Adverse Drug Reactions (PREPARE) study, is one of the largest efforts to evaluate PGx in a real-world setting.

This randomised trial involved 6,944 patients, in multiple clinics across seven countries, who needed one or more of 42 medications for many different conditions. A 12-gene PGx panel was used to inform the prescribing decisions for one group of patients; the other patients had treatment as usual i.e., no PGx test. The study demonstrated that having the PGx information reduced a patient’s chance of a significant adverse drug reaction by one-third compared to a patient who had received treatment as usual.

Professor Graeme Suthers, an Australian genetic pathologist, said, “One of the major barriers preventing the widespread use of PGx testing has been the lack of evidence to support it. Until now, the benefit of PGx testing using single-gene drug combinations has been demonstrated, but the use multi-gene panels has not been thoroughly assessed. This trial is a huge step forward as it provides strong evidence to support the large-scale implementation of pre-emptive, multi-gene PGx testing to improve the safety of drug therapy.

Potential of PGx testing

“It is important to understand the potential of PGx testing on improving patient outcomes and its effect on prescribing practice. In Australia, around 250,000 hospital admissions annually are a direct result of medication-related problems, with an annual cost of $1.4 billion to the healthcare system. This trial shows that we could potentially prevent one third of those adverse reactions to a medication. By predicting a patient’s response to medications using PGx testing, it is possible to make medications safer, reduce hospitalisations and reduce costs,” said Prof Suthers.

An adverse reaction to a medication can cause anything from mild discomfort to a severe, potentially fatal crisis. Severe reactions are fortunately uncommon, but the personal cost and need for expensive care are prompting greater awareness of PGx as a means of avoiding some of these reactions.

Recent commentary articles in the Medical Journal of Australia have highlighted the potential for reducing the chance of severe bone marrow failure or of a severe blistering reaction to various widely prescribed medications. The chance of the average patient having such a reaction is low, but a PGx test can accurately identify those individuals who have a much greater chance of having such a reaction. Such patients can be treated with a drug or dose that differs from the usual treatment. Both articles called for a national response to make such PGx testing readily available.