The transdermal patches for site-specific delivery of letrozole: a new option for breast cancer therapy.

The aim of this work was to evaluate capability of site-specific delivery of a transdermal patch through determination of letrozole in local tissues disposition in female mice. After transdermal administration, the letrozole levels in skin, muscle, and plasma were 10.4-49.3 μg/g, 1.64-6.89 μg/g, and 0.35-1.64 μg/mL, respectively. However, after the mice received letrozole suspension, the drug concentration of plasma and muscle were 0.20-4.80 μg/mL and 0.15-2.38 μg/g. There was even no drug determined in skin through all experiments. Compared with oral administration, the transdermal patch for site-specific delivery of letrozole could produce high drug concentrations in skin and muscle and meanwhile obtain low drug level in plasma. These findings show that letrozole transdermal patch is an appropriate delivery system for application to the breast tumor region for site-specific drug delivery to obtain a high local drug concentration and low circulating drug concentrations avoiding the risk of systemic side effects.