April 24, 2000 -- A newly developed breath test may be the first step toward making chemotherapy safer and more effective.
Each of our bodies breaks down, or metabolizes, drugs at a different rate. Those whose bodies eliminate the drug slowly may be more likely to be sickened, or even die, from their treatment, while those who process the drug too quickly may not reap the full benefit. The new test measures how much of a certain liver enzyme -- the molecule that digests a drug -- each patient has.
"Some people have a lot of the enzyme and move drugs quickly through the pathway, and others have only a little and move drugs more slowly," says Paul B. Watkins, MD. Watkins is professor of medicine and director of the Verne S. Caviness General Clinical Research Center at the University of North Carolina at Chapel Hill.
Until now, determining an individual's enzyme level required a tissue sample from the liver or a cumbersome, time-consuming study. This new test, however, can be done just prior to receiving the chemotherapy and only requires that the patient exhale.
Co-author Laurence Baker, DO, tells WebMD that the test is based on the fact both the common antibiotic erythromycin and the potent chemotherapy drug docetaxel are metabolized by the same enzyme in the liver. Presumably, he says, "by measuring how efficiently a patient metabolizes erythromycin, you could also predict how efficiently they will metabolize docetaxel," and adjust their dosage accordingly. Baker is director of clinical research at University of Michigan Comprehensive Cancer Center.
"I came up with a cute trick that enables doctors to give a dose of erythromycin, collect a single breath sample 20 minutes later, [and] determine the rate at which docetaxel will be [metabolized]," says Watkins.
The team studied 21 male and female cancer patients. They gave each patient a breath test before beginning the study, one hour before taking docetaxel, and again three hours afterward.
Patients who got sickest from the docetaxel also had the lowest levels of erythromycin in their breath tests. The findings go a long way toward explaining the "wide range of reactions" that doctors are accustomed to seeing with this and other chemotherapy agents, says Baker.
The research is published in the April issue of the journal Clinical Cancer Research.
Based on these results, says Baker, the team has already begun additional trials in breast cancer patients. "We've developed a formula [where] the dose is [based on] the breath test," he says.
According to Baker, "this is the first time that you can make the dose of a cancer drug individualized to the patient. It's easy to see how this will make chemotherapy less toxic. And hopefully, those who can tolerate more than the normal dose may respond even faster or better [to a higher dose]." What's more, he tells WebMD, custom-tailored dosing may allow safe, potentially life-saving treatment for those with very advanced disease.
Jerry M. Collins, PhD, the director of the laboratory of clinical pharmacology at the FDA, agrees in an accompanying editorial. "It is rapid, relatively noninvasive, requires only a single time point and can be used prospectively before dosing," he writes. He finds the test to be "a very promising approach."
- The amount of time it takes a patient's body to process a drug and remove it is different from person to person. Patients can become ill or even die if they process chemotherapy medicines more slowly than doctors would expect them to.
- A new breath test may give doctors a better idea about how long a chemotherapy medicine would remain in a patient's system. The test works by introducing a milder drug and testing the patient's breath for how much of a protein the patient's body has that breaks down the drug. Because the same protein, or enzyme, is used to process the chemotherapy drug, doctor's get a better idea of how well the patient can handle it.
- The researcher notes this test will help doctors adjust the amount of chemotherapy a patient gets in order to maximize benefits while controlling side effects.