Transdermal delivery of pharmacologically active agents has been extensively studied for the past 40 years. Despite the strong efforts, currently, only about 40 products are in market on about 20 drug molecules, due to the requirements that the patch area should be small enough for the patients to feel comfortable, and to the barrier properties of the stratum corneum. Various approaches to overcome the barrier function of skin through physical and chemical means have been broadly studied. The development of an effective transdermal delivery system is dictated by the unique physicochemical property each drug molecule possesses. In this review, we have summarized various physical and chemical approaches for transdermal flux enhancement, including the application of electricity, ultrasound, microneedle and chemical enhancers. Pressure sensitive adhesive such as acrylics, rubbers and silicones are described together with recent developments. Factors affecting dosage form design, particularly for drug in adhesive system, like adhesion and crystallization are also discussed.

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Cryptotanshinone, tanshinone I and tanshinone IIA are three major components in the extract of Salvia miltiorrhiza with pharmacological significance. However, their effective utilization is limited due to poor water solubility and bioavailability. Solid dispersion (SD) of the extract of Salvia miltiorrhiza was prepared to enhance solubility and dissolution of the three major components. Various carriers were screened for SD preparation by conventional solvent method. Dissolution of the components from selected SD systems was compared with commercial tablets of the extract from Salvia miltiorrhiza. The solubility of three components viz., cryptotanshinone, tanshinone I and tanshinone IIA, after forming SD with either of povidone K-30 (PVP K-30) or poloxamer 407, exhibited enhanced solubility in pH 6.8 buffer. Dissolution test revealed that the amount of three components released was higher from SD tablets as compared to the commercial tablets. Pharmacokinetic profile was evaluated using cryptotanshinone as a representative compound. AUC of cryptotanshinone was significantly increased when administered as a solid dispersion.