When you enter a Chemmart pharmacy, it’s hard to miss the
posters and brochures promoting its “revolutionary myDNA
test”. The brochure states that it’s “personalised medicine”
where “your DNA results ... can help guide your future health
and lifestyle choices”.
Advertising on both the Chemmart and myDNA websites
claims that “70% of people who take the test have a inding
that could affect current or future medications”.
It’s said you should consider the test if you’re taking anti-
depressants, pain or relux medication. The test also covers
those who take blood thinners such as warfarin. It’s said to be
particularly relevant if you have a history of not responding to
common drugs, you experience side-effects from your current
medication, you take multiple medications, you have children
on prescribed medication, or you are pregnant or planning preg-
nancy.
The test identiies common variations in the genes encoding
some enzymes that metabolise a number of drugs (Table 1).
Table 1.
Enzyme Common potentially actionable drugs metabolised
CYP2C9 Warfarin, phenytoin
CYP2C19 Tricyclic antidepressants, clopidogrel, SSRI antidepressants, Protein pump
inhibitors (PPIs) for gastro-oesophageal reflux, e.g. esomeprazole
CYP2D6 Codeine, tramadol, tricyclic antidepressants; SSRI antidepressants
VKORC1 Warfarin
The test costs $149 but is not covered by Medicare or private
health insurance rebates. It involves a cheek swab taken by a
trained pharmacist that is sent to a lab for DNA analysis. The
pharmacist receives $15 per test, with $30 going to Chem-
mart and the rest to myDNA. The results are delivered by a
personal consultation with the trained pharmacist and are also
sent to your nominated doctor. If changes to medication are
recommended you will be referred by the pharmacist to your
doctor.The Science
Pharmacogenomic/genetic (PGx) tests are moving from scien-
tiic discovery to clinical implementation. Inherited variation
in approximately 20 genes affecting around 80 medications
may predict a patient’s likelihood of experiencing an adverse
event (e.g. through poor metabolism of some drugs) or non-
responsiveness to a given drug due to ultrarapid metabolism.
However, the cost-effectiveness and clinical utility of these
tests is still uncertain. In addition, the scientiic basis of the role
of genes in the response to drugs is incomplete and rapidly changing.
A “normal” PGx test does not necessarily mean that you are
not at risk for adverse events or non-response because currenttests only capture known variants of known genes. Different
companies providing these tests may report on different sets
of known gene variants, and validation of laboratories and regu-
latory oversight in Australia is incomplete.
More traditional considerations, such as drug–drug inter-
actions, drug allergy and dosing taking into account age, body
weight, renal and liver function are still more important in opti-
mising therapy than genetic considerations. In addition, many
GPs currently have limited understanding of how to interpret
such tests.
The blood thinner Warfarin is one example. Some studies
have shown a reduction in adverse effects when starting doses
of warfarin were changed by taking into account genetic vari-
ations of CYP2C9 and VKORC1, but the results have been
mixed. At present, routine use of a genetic test to guide warfarin
dosing is not recommended.The Verdict
I believe Chemmart has overstated the role and value of this
test. Instead of the broad claim that “myDNA is a genetic test
that identiies which medications will work best for you,” I
think they should have pointed out that the test is only appli-
cable to certain drugs in particular situations.
I dispute that the test is “particularly relevant” to those who “take
multiple medications, have children on prescribed medication”
or “are pregnant or planning pregnancy”. These concerns have
been submitted to the Therapeutic Goods Advertising Complaint
Resolution Panel for an independent determination.
At present, the routine use of genetic tests to guide drug dosing
is not recommended. Consumers should discuss the usefulness
of this test with their GPs before handing over their $149.
Ken Harvey is an Adjunct Associate Professor in the School of Public Health and Preventive
Medicine at Monash University, and an executive member of Friends of Science in Medicine.46 | APRIL 2016
THE BITTER PILL Friends of Science in MedicineIs Chemmart’s myDNA Test Right for You?
The promises of genetic tests and treatments may be outstripping the science.The front page of the Chemmart myDNA brochure, which is
freely available from Chemmart pharmacies.