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Patrick Guilfoile: Mind your microbes when you take your medicine

One-size-fits-all gloves work well for most people, but for some, these gloves are either too tight or too loose. In much the same way, standard doses of medicine work well for most people. Yet there are some individuals who, on standard doses of drugs, don't get enough medicine to treat their symptoms, and other people who have damaging side effects from elevated levels of the same drug.

Some of these differences in the response to the same dose of a drug are the result of genetic factors. Some people have alterations in their DNA that lead to higher or lower levels of the drug circulating in their bloodstream. For example, there are genetic differences in patients that can lead to reduced effectiveness of certain blood thinning medications. Some individuals end up with higher than normal levels of the blood thinners that make them prone to excessive bleeding. Other individuals, because of their genetic makeup, end up with lower than expected levels of blood thinners, and this can increase their risk of stroke and heart attack.

In a recent article, scientists from Harvard University identified another factor that can reduce the effectiveness of a drug. In the case of the heart drug digoxin, a specific microbe in the gut can break down this compound. People with certain strains of this bacterium may have a lower concentration of the drug than others who lack the microbe. Consequently, this medicine may be less effective, or require a higher dose for these individuals. The researchers also grew these microbes in the lab, to get a better idea of what turned off the bacterium's drug-degrading machinery. They found that a high protein diet for the microbes damped down their ability to break down digoxin. Consequently, eating lots of protein may help bring the drug concentration backup in patients with this particular bacterium in their intestines.

This new information helps explain why some people benefit more by digoxin than others do, and illuminates the complexity in determining the appropriate dose of this drug. It is likely that additional cases of the detailed role of microbes in modulating the effectiveness of various drugs will be uncovered, as more than 40 drugs are known to be chemically changed by intestinal microbes. In the future, it is possible that many medications will include instructions that will recommend a specific diet, based on our microbial flora, in order to better control the effects of medicines that we take.

More information is available in an article by Henry Haiser and others "Predicting and manipulating cardiac drug inactivation by the human gut bacterium Eggerthaella lenta." in Science, Vol 341, pages 295-298, July 19, 2013.

PATRICK GUILFOILE has a Ph.D. in bacteriology and is the associate vice president at Bemidji State University.