Richard Dawkins, the British biologist, once said "DNA neither cares nor knows. DNA just is. And we dance to its music." If, by dancing, he includes the way in which individual people metabolize drugs, then clearly as pharmacists we need to be thinking about the music going on inside our patients' cells.

The study of the pharmacologic implications of gene variations, also known as pharmacogenomics, is a rapidly growing and exciting area of our profession. As such, all pharmacists need to have some foundational awareness of the various (and sometimes dangerous) responses to drug therapy that are based upon the genetic makeup of a patient.

The focus on this field is growing. A JAMA article just published Sept. 21, entitled "Getting Pharmacogenomics Into the Clinic," highlights some of the key advantages to gaining more insights into a patient's genetics prior to prescribing certain medications.

In that article, Dr. Mary Relling, chair of the pharmaceutical sciences department at St. Jude's Children's Research Hospital said, "Genetic variability affects essentially every single gene in the human genome, and sometimes it's going to affect genes whose proteins are critical for drug response."

And it is not just the academic literature that is talking about these variations in responses to drugs based on personal genetics. A Wall Street Journal article in May — "Is Your Medicine Right for Your Metabolism?" — is an example of how awareness of this important topic is expanding rapidly even among patients.

The author of this article tells the story of a 75-year-old woman, Elise Astelford, who "experienced hallucinations, a deep depression and symptoms of dementia while taking various drugs over the years. After spotting a newspaper ad for gene testing, she convinced her primary care doctor to order it. She learned she has variations in three key liver enzymes that make her an intermediate metabolizer of dozens of common drugs."

So what sorts of drugs are we talking about that exhibit such variations in effect and metabolism based upon individual genetics?

Currently, there are about 120 prescription drugs in which the official FDA labeling information carries warnings or precautions related to genetic variations in patients.

Examples include some commonly prescribed drugs like codeine. A gene known as CYP2D6 is responsible for metabolizing codeine into morphine, which in turn produces the pharmacologic analgesic response.

But upwards of 2 percent of all people have a CYP2D6 variation resulting in them being ultra-rapid metabolizers of codeine, leading to much higher than expected morphine blood levels. This phenomenon is dangerous and even fatal, especially in children. Recognition of this fact led the FDA to require a boxed warning and contraindication for the use of codeine in children after tonsillectomies.

Clopidogrel is another commonly prescribed medication for which genetic variations in metabolism can impact the effectiveness of the drug. A boxed warning on the labeling of this medication states the "effectiveness of clopidogrel depends on activation to an active metabolite by the cytochrome P450 system, principally CYP2C19" and that poor metabolizers treated with this drug "exhibit higher cardiovascular event rates following acute coronary syndrome or percutaneous coronary intervention than patients with normal CYP2C19 function."

This genetically determined response to clopidogrel was actually the subject of a lawsuit filed by David Louie, attorney general in Hawaii. He argued that Bristol-Myer Squibb and Sanofi-Aventis failed to sufficiently educate people on this important genetic variation which is quite common among Pacific islanders.

Other commonly prescribed medications for which the effectiveness or safety can vary based upon genetic factors include allopurinol, amitriptyline, carbamazepine, citalopram, imipramine, phenytoin, simvastatin, warfarin and many more.

Peter H. O'Donnell, M.D., who is the associate director for clinical implementation at the University of Chicago's Center for Personalized Therapeutics said, "It is likely that a time will come in the near future where patients will start to demand the use of such information during care — that they will ask of their physician, 'Have you considered my genomics?' before accepting a prescription."

Of course, adoption of DNA testing for genetic variations has been slow. But the growing awareness of the importance may put pressure on providers and insurance plans to make such testing more commonplace. Already there are companies that are bringing genetic testing directly to consumers.

Although Dawkins may be right that our DNA "neither cares nor knows," the same shouldn't be said for us as pharmacists when it comes to genetic responses to prescription medication. We need to care, and we ought to know.