A Comprehensive Review on Transdermal Drug Delivery Systems: Principles, Formulation, Evaluation, Recent Advances and Future Perspectives

Transdermal Drug Delivery Systems (TDDS) have emerged as an effective and patient-friendly approach for delivering medications through the skin into the systemic circulation. These systems provide several advantages over conventional oral and injectable dosage forms, including avoidance of first-pass metabolism, sustained drug release, improved bioavailability, reduced dosing frequency, and enhanced patient compliance. The skin, while serving as a protective barrier, also presents challenges to drug permeation, making the understanding of skin structure and permeation mechanisms essential for successful transdermal formulation development.This review highlights the fundamental principles of transdermal drug delivery, including skin anatomy, pathways of drug permeation, and factors influencing drug absorption through the skin. It discusses the ideal characteristics of drugs suitable for transdermal administration, key formulation components such as polymers, adhesives, permeation enhancers, and backing membranes, as well as various preparation methods and evaluation parameters used in the development of transdermal patches. The review further explores therapeutic applications of transdermal systems in pain management, cardiovascular disorders, hormone replacement therapy, neurological conditions, and smoking cessation.Recent advancements involving nanotechnology-based carriers, microneedles, iontophoresis, sonophoresis, electroporation, and smart wearable drug delivery devices have significantly expanded the potential of TDDS. Despite certain limitations, including restricted drug selection and skin irritation concerns, continuous technological innovations are improving the efficiency and versatility of transdermal delivery systems. Overall, TDDS represent a promising and rapidly evolving drug delivery platform with significant potential to enhance therapeutic outcomes and support the future of personalized medicine