Sunlight linked to drug`s effectiveness

Last Updated: Mar 10, 2011, 00:00 AM IST

London: The effectiveness of any drug in a body may be closely linked with exposure to sunlight and may vary seasonally.

The findings offer a completely new model to explain individual differences in the effects of drugs, and how the surroundings can influence the body`s ability to deal with toxins.

The study by Karolinska Institutet in Sweden is based on nearly 70,000 analyses from patients who have undergone regular monitoring of drug levels in their blood, the journal Drug Metabolism and Disposition reports.

The drugs taken by these patients were used to suppress the immune system after organ transplants. Samples taken during the winter months were compared with those taken late in the summer.

A more detailed analysis showed that the concentrations of drugs such as tacrolimus and sirolimus, to prevent rejection following transplantation, vary throughout the year in a manner that closely reflects changes in Vitamin D levels in the body, which is dependent on sunlight.

The connection between sunlight, Vitamin D and variations in drug concentration is believed to arise from the activation by Vitamin D of the detoxification system of the liver by increasing the amount of an enzyme known as CYP3A4.

This enzyme, in turn, is responsible for the breakdown of tacrolimus and sirolimus.

"If the breakdown capacity (of medicine) increases, then higher doses of a drug are normally required in order to achieve the same effect," says Jonatan Lindh, study co-author from Karolinska Institutet.

IANS