Liquid Transdermal Drug Delivery: The State of the TDS® Art

To date, transdermal delivery has been effective in delivering only a very few drugs due to diffi culties in moving larger, and chemically non-compatible, molecules across the skin’s biologically-active barrier. Drugs with higher melting points, drugs of molecular weight greater than 500 Daltons and drugs requiring pharmacological doses of more than 40 mg in 24 hours can not employ patchor gel-based transdermal delivery as a safe and effective modality. More recently, alternative approaches have been attempted to expand possibilities, employing various devices and modalities, such as micro-needle arrays in patches, or phonophoresis or iontophoresis to breach what is designed to keep the outside out and the inside in. While the avoidance of toxicity and side-effects is a major motivator in the quest for a liver fi rst-bypass delivery modality, until now a truly fl exible, convenient enabler of transdermal dosing has been lacking. This article discusses developments in this mode of delivery made by TransDermal Technologies, Inc. (TTI) with its patented TDS® liquid spray-on delivery technology.