Tailoring Chemo Drugs to Fit Your Body

Tailoring Chemo Drugs to Fit Your Body with Pharmacogenetics
December 11, 2017

How do you know if the drug your doctor prescribed is working?

It might not be.

A blossoming area of precision medicine, particularly for cancer, is therapeutic drug monitoring (TDM), where laboratory tests can show if and how a person is metabolizing a drug. Part of pharmacogenetics testing, TDM delves into a person’s DNA to determine one aspect of a drug’s likelihood for efficacy.

Traditionally, clinicians have depended on the weight and height of a patient to determine the best dose, also known as body surface area (BSA). However, there is no rigorous scientific basis for the use of BSA with cancer drugs.

When it comes to metabolizing drugs, we’re not all the same. Consider how one person can drink a cup of coffee after dinner and sleep like a baby, while someone else can’t sleep a wink after eating a bowl of coffee ice cream. Each person metabolizes the caffeine differently.

This is also true with chemo drugs—and a lot more is at stake than a good night’s sleep. Too much of a chemo dose can result in severe side effects; too little and the cancer sticks around.

A lot of oncologists have not embraced therapeutic drug monitoring. They will dose patients based on body size or push the dose as far as the patient can tolerate.

Gwen McMillin, PhD, ARUP medical director

For chemo drugs, like imatinib, which can be taken orally at home, a simple blood test can show how a patient’s body is handling the drug and if they are taking the medicine as prescribed. A patient may stop taking medication for a number of reasons—they may forget to take it; avoid it due to side effects; start feeling better so they think they can stop taking it; or can’t access the drug (i.e., financial or physical limitations).

“There are very few drugs where oncologists have optimized the dose,” says Gwen McMillin, PhD, medical director of Toxicology and Pharmacogenetics at ARUP. “A lot of oncologists have not embraced therapeutic drug monitoring. They will dose patients based on body size or push the dose as far as the patient can tolerate.”

Imatinib is an ideal drug for optimizing since it has been well researched to determine the ideal therapeutic target—how much the body needs for it to work. It has also revolutionized treatment for chronic myeloid leukemia (CML), prolonging life expectancy from two–five years to that of the general population. Imatinib (the generic name for Gleevec) is also used to treat gastrointestinal stromal tumors and melanoma.

“One of the challenges is there are alternative drugs. Oncologists will try one drug, and if it doesn’t work, they’ll switch to another drug rather than finding out why,” explains McMillin. Decisions can also depend on affordability or insurance coverage for a particular drug.

Ask your doctor if there is a test to help determine if a medication will or is working well with your body. Such pharmacogenetic tests help doctors monitor if patients are complying, find the ideal dosage, and also evaluate reasons for resistance to the drug. For a test like the Imatinib Plasma Test, it starts with a simple blood draw, and the answers will follow.

Peta Owens-Liston, Science Communications Writer


Related blog:

Advancing Precision Medicine Through Pharmacogenetics: Updated Test Prevents Adverse Drug Reactions

Drug Monitoring: One Approach to Decreasing Addiction


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Pharmacogenetics of CYP-mediated drug metabolism