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A photo of Timothy Tracy.

U professor Timothy Tracy's latest study shows that dosage adjustments depend on the stage of pregnancy and the medication.

One size does not fit all

By Amy Danielson

From eNews, September 29, 2005

When a physician writes a prescription for a patient, the dose is often based on studies that until recent years have been conducted exclusively on healthy men. This could pose a problem for women, whose bodies process medications differently than men's. Pregnant women are of even greater concern, as their bodies metabolize different drugs at different rates during each trimester. As healthy women are now included in dosing studies, researchers at the University of Minnesota are looking at the unique needs of pregnant women.

Timothy Tracy, a professor in the Department of Experimental and Clinical Pharmacology, has published findings that will help pregnant women receive the right dose of medication to manage chronic conditions such as diabetes, depression, or HIV during each stage of pregnancy. Tracy notes that a pregnant woman's ability to metabolize medications depends on the stage of pregnancy and the medication taken--dosages can't be determined by a one-size-fits-all approach. "The dose a woman needs in pregnancy may need to be changed throughout her pregnancy," he says.

Researchers knew pregnant women needed to have their medications adjusted, but they didn't know by how much and whether to increase or decrease dosages. Tracy's findings show that dosage adjustments depend on the stage of pregnancy and the medication.

"You can't treat all medications the same," Tracy says. "You can't say 'She's pregnant so we automatically have to increase or decrease the medication.'"

In the study, pregnant women were given two drugs known to be safe during pregnancy--caffeine and dextromethorphan, a cough suppressant that is available without a prescription. These are considered "marker drugs" since they are broken down by specific enzymes in the body. The women were given the drugs three times: between the 14th and 18th weeks, between the 24th and 28th weeks, and between the 36th and 40th weeks of pregnancy. They were also given the drugs between six and eight weeks after giving birth.

Three enzymes in the body metabolize about 80 percent of medications--including caffeine and dextromethorphan. Tracy studied the concentration of these drugs after they were ingested to determine whether the metabolism of the medication increased or decreased throughout pregnancy.

Tracy found that in general pregnant women's metabolism of some medications increases or decreases only once during pregnancy, while metabolism of other medications continues to increase or decrease as pregnancy progresses. The change depends on which enzyme the body uses to metabolize the drug. Researchers can now correlate the findings to the 80 percent of medications metabolized by these enzymes. That means more accurate and safer dosing guidelines for medications women need to manage their chronic conditions as their bodies change during pregnancy.

The findings from Tracy's research were published in the February issue of the American Journal of Obstetrics and Gynecology.

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