In vivo kinetics of magnetically targeted low-dose doxorubicin

The in vivo kinetics of low-dose doxorubicin (0.05 mg/kg), entrapped in a carrier and magnetically targeted, were characterized in a rat tail model. Tissue concentrations of doxorubicin at a preselected target site and in various organs were followed over time. As late as 60 min postinjection, 3.7 microgram/g of drug was found at the target site with no detectable drug levels found in any organ. In comparison, a 100-fold higher dose (5.0 mg/kg iv) of free doxorubicin yielded drug concentrations of 1.8 microgram/g at the target site and 15.0 microgram/kg in the pooled organs. Therefore, 1% of the free intravenous dose targeted magnetically yielded approximately twice the local doxorubicin concentration at a preselected target site with no detectable systemic distribution. Magnetic targeting of particulate drug carriers to localized disease sites is suggested as an efficient method of obtaining high local drug concentrations and may reduce many unwanted side effects from unrestricted systemic circulation.