Cold flow measurement of transdermal drug delivery systems (TDDS)

Cold flow, the movement of adhesive beyond the edge of a transdermal drug delivery system (TDDS) or between the release liner slit, can affect the quality of the drug product and result in patient use issues such as difficulty in removal from packaging and unintentional removal of the product during wear due to increased tackiness on the edge and backing of the TDDS. In this study, different techniques for measuring cold flow of United States marketed transdermal drug delivery systems are assessed including a wiping method with various ways of calculating cold flow, a macroscopic rating method and a microscope evaluation. The amount of cold flow measured from the wiping method was dependent upon the calculation method. Assessment of cold flow may be a combination of quantitative and qualitative methods. Appearance criteria can assess potential use issues caused by cold flow if TDDS are difficult to remove from pouches and if release liners detach from the adhesive matrix during attempted removal due to cold flow adhering the backing to the pouch. A quantitative cold flow method captures the degree to which cold flow extends beyond the perimeter of the backing and through the release liner slit. The method(s) selected by a TDDS manufacturer to measure cold flow should be applicable to the individual product and scientifically justified.