When you enter a Chemmart pharmacy, it’s hard to miss the posters and brochures promoting its “revolutionary myDNA test”. The brochure states it’s “personalised medicine”, where “your DNA results … can help guide your future health and lifestyle choices”.
It’s an enticing promise. Knowing your genes unlocks a healthier future. Right?
The promotional materials suggest taking the test if you’re using antidepressants, pain or reflux medication. The test also covers the common, but difficult to manage, blood thinner warfarin, which is prescribed to approximately 30% of patients over the age of 70 years.
Chemmart says it’s particularly relevant if you have a history of not responding to common drugs, you experience side-effects from your medication, you take multiple medications, you have children on prescribed medication, or you are pregnant or planning pregnancy.
But some of Chemmart’s claims may be misleading for consumers who lack detailed knowledge of DNA testing and may produce unrealistic expectations of the product’s effectiveness. In so doing, Chemmart appears to have breached a number of provisions of the Therapeutic Goods Advertising Code 2015.
The test costs A$149 and is not covered by Medicare or private health insurance rebates. It involves a cheek swab taken by a trained pharmacist, which is sent to Australian Clinical Labs (formerly Healthscope Pathology) for DNA analysis.
The results are delivered by personal consultation with the pharmacist and are also sent to your nominated doctor. If the pharmacist recommends changes to medication, you are referred to your doctor.
As part of their training, participating pharmacists are encouraged to explain the test to local doctors, both to educate them and prepare them for pharmacist referrals or enquiries from patients.
The test identifies common variations in four genes that are involved in processing a number of drugs. For example,
CYP2C9 and VKORC1 affect the metabolism of the blood-thinning drug warfarin
CYP2D6 is involved in the metabolism of the pain killers codeine and tramadole, as well as antidepressants
CYP2C19 affects the metabolism of antidepressants, the newer blood thinner clopidogrel and drugs taken for reflux, such as esomeprazole.
The term pharmacogenetics was first coined in 1959 but it is only recently that pharmacogenetic (PGx) tests have moved from the lab to the clinic.
Researchers have now identified inherited variation in approximately 20 genes affecting around 80 medications, which are potentially actionable in the clinic.
Genetic variations may predict, for example, that a patient is at increased risk of experiencing the side-effects of certain drugs because they metabolise it slowly and high concentrations can build up on a normal dose.
Other genetic variations may cause a particular drug to be metabolised too rapidly, so patients may need a higher dose of the drug to achieve a therapeutic effect.
But a “normal” PGx test doesn’t mean you’re not at risk of drug-related side-effects or of not responding to a drug. Current tests only capture known variants of known genes.
And even if the test shows gene variants that impact on a certain drug’s metabolism, this is only one of many patient characteristics and factors that influence how they respond to drugs. Others include interactions with other drugs, allergies, and kidney and liver function.
As a result, the cost-effectiveness and clinical utility of PGx tests is still uncertain.
Case study: warfarin
Warfarin is a commonly prescribed blood-thinning drug that prevent strokes in patients who have an irregular heartbeat or whose heart valves have been replaced. However, it must be monitored closely with regular clotting tests to ensure it is at the right therapeutic level to prevent bleeding or stroke.
Variations in the genes VKORC1 and CYP2C9 can either slow warfarin metabolism, thereby increasing the risk of bleeding, or increase sensitivity, which may require a lower dose to produce the required effect.
However, in practice, the clinical implementation of genetic testing for warfarin dosing has been disappointing. The current consensus guidelines by the American College of Chest Physicians actually warn against the routine use of genetic data to guide dosing because of its poor predictive value for large populations.
Chemmart claims “myDNA is a genetic test that identifies which medications will work best for you”. This overstates the role and value of this test.
It has limited applicability only to certain drugs in particular situations.
We do not believe the test is “particularly relevant” to those who “take multiple medications, have children on prescribed medication”, or “are pregnant or planning pregnancy” because of the extremely limited applicability of the test to these patient groups.
We also have problems with the claim that “the myDNA test covers 50% of the most commonly prescribed medications”. This is not in accord with data from the United States, which shows that just 7% of approved medications and 18% of outpatient prescriptions are affected by actionable pharmacogenes (genes you can test for and alter medication around). Nor is it in accord with Australian data on the top ten drugs prescribed.
We have submitted our concerns to the Therapeutic Goods Advertising Complaint Resolution Panel for an independent determination.
More research (and GP training) will be required to determine if PGX tests improve patient care and are cost-effective. In the meantime, marketing claims should reflect the current uncertain clinical role of these tests.
The role of test providers, pharmacists and doctors
Before undertaking PGx tests, which are also available from other providers, the National Health and Medical Research Council recommends discussing their value and applicability with your GP.
Pharmacists play an important role in engaging with consumers and doctors to achieve better use of medication. But the current model of pharmacist “detailing” PGx tests has several problems. “Detailers” are not welcomed by all GPs. Some clinics have demanded the pharmacist bring a free lunch (often provided by drug reps) before they will schedule a visit.
Finally, the national prescribing service NPS Medicinewise has an important role to play in developing a pharmacogenetic education campaign. This could still involve trained pharmacists but NPS Medicinewise authority would provide greater access to GPs without the demand for lunch as the price of entry.