Genetic Testing & Drugs

Pharmacogenomics: Determining the most effective drug for your genetic makeup.

Each person is unique and so is his or her response to certain medications.  Since the mapping of the Human Genome Project was completed in 2003, a new area of study and research has opened up called, Pharmacogenomics, the technology that analyses how genetic makeup affects an individual’s response to drugs—will a drug be helpful for a specific treatment or will it be toxic? Will it help or hinder? Will you be at increased risk for certain side affects or will genetic testing help to avoid a serious adverse drug reaction.

Such approaches promise the advent of personalized medicine in which drugs and drug combinations are optimized for each individual’s unique genetic makeup.

There are two areas  pharmacogenomics is being applied.  One is in the area of cancer treatment and the other is using genetic testing to determine response to certain medications.

In the area of cancer treatment, oncologists may order certain tests that will look at the genetic features of a tumor to assess how the cancer will respond to certain types of treatment and what form of therapy would be best for a particular patient.  This is the only area today that may be covered by health insurance in Ontario.

The other use for genetic testing is in the area determining the effectiveness of certain drugs for treatments related to heart disease such Plavix or Warfarin.

We have learned that the uniqueness of our genetic makeup means that not all drugs work in the same way for all individuals or it may be hard to get the dose right.   It is not yet common practice in Canada or covered under OHIP, but genetic testing in this area can be carried out privately if your doctor determines it is warranted.  Ideally, Medisys genetic counselor, Katherine Hodson, suggests the test be carried out before a drug such as Warfarin or Plavix is prescribed to avoid adverse reactions and ensure the right dosage.

Genetic testing may also be used to determine whether certain pain relievers such as codeine will work well for a given patient.  An individual suffering from chronic pain may not respond to codeine as genetically, that person may metabolize the drug too quickly.  In this case, the patient would need a different medication and of course, given concerns about narcotics and drug seeking, how reassuring it is to have a clear medical answer about different or higher dosing requirements.

We are on the cusp of understanding more about genetics, medications, reactions, both good and bad, and that will make prescribing drugs much more personalized, with predictable and better outcomes.

Dr. Vivien Brown, MDCM, CCFP, FCFP, NCMP,
Vice-President, Medical Affairs, Medisys Health Group