Drugs Affected by Sunlight

Vitamin D causes body to break down organ transplant drugs

(RxWiki News) Sunlight activates the body's stores of vitamin D, a vitamin shown to be beneficial to the immune system, bone health, and even in fighting cancer. New research shows that sunlight can also affect how the body deals with drugs.

The study's findings have implications for determining effective drug dosages for patients following organ transplants.

Using data from almost 70,000 analyses, researchers at Karolinska Institutet in Sweden found that exposure to sunlight may have an impact on the body's ability to break down medications, specifically medications that are used to suppress immune system responses after organ transplants.

dailyRx Insight: Vitamin D may reduce the effectiveness of transplant rejection drugs.

Jonatan Lindh, from the Department of Laboratory Medicine at Karolinska Institutet, and colleagues examined levels of drugs in the blood of organ transplant recipients during both winter and summer. They then compared those drug levels to the amount of vitamin D found in patients bodies at those same points of the year.

They found that the concentrations of drugs such as tacrolimus (Prograf®) and sirolimus (Rapamune®) - drugs used to prevent the body from rejecting transplanted organs - in the bodies transplant recipients changed throughout the year. These changes followed a similar pattern to the changes in vitamin D levels in patients' bodies.

The researchers believe that the relationship between sunlight, vitamin D, and differences in drug concentration is the result of vitamin D's role in liver function. Vitamin D activates an enzyme called CYP3A4, which increases the detoxification functions of the liver. This enzyme is responsible for breaking down tacrolimus and sirolimus.

In other words, as exposure to sunlight increases, so do levels of vitamin D. As levels of vitamin D increase, the liver works harder to break down tacrolimus and sirolimus.

As liver's ability to breakdown drugs intensifies, then it may be necessary to increase drug doses in order to achieve the same results, says Lindh. Although more research is needed to confirm this study's findings, it is likely that vitamin D's effect on the CYP3A4 enzyme will have an impact on drug treatments for organ transplant recipients. Furthermore, the study provides some insight into why some individuals react differently than others to drug treatment.

The study will be published in Drug Metabolism & Disposition.

Review Date: 
March 9, 2011