Induction and Inhibition of Crystallization in Drug-in-Adhesive-Type Transdermal Patches

Purpose

To screen crystallization inhibitors, perform accelerated stability testing and predict saturation solubility of levonorgestrel in drug-in-adhesive patches.

Methods

Differential scanning calorimetry (DSC) studies were compared against slide crystallization studies for screening additives. Release studies were performed from crystallized and supersaturated patches. Die cutting was used for accelerated stability testing of patches. Time lag experiments were performed to predict saturation solubility of levonorgestrel in acrylate adhesive, DuroTak-2516.

Results

DSC studies indicated poloxamer to be the best additive whereas slide crystallization studies showed polyvinylpyrrolidone to be better. Supersaturated patches showed higher release profiles relative to crystallized patches. Crystals were observed in crystallized patches even after 96 h of release studies. Die-cutting of patches helped in development of crystals in less time as compared to uncut sheets indicating its usefulness in accelerated stability testing. Saturation solubility of levonorgestrel in DuroTak-2516 was predicted to be 0.09% w/w which was in close agreement with value of 0.1% w/w from solubility calculator on vendor’s website.

Conclusions

Crystallization was shown to have negative impact on drug release and patch performance. Slide crystallization studies, die cutting and time lag experiments can be used as tools to help stabilize the otherwise unstable patches.