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The research in therapeutic systems has increased quickly with the development of new materials and new mathematical approaches, and further application of physicochemical tools. Moreover, the great development of biotechnology and the understanding of physiological mechanisms have enabled the possibility of designing dosage forms that are each more specialized. This is increasing the number of strategies that can be applied to develop systems with enhanced properties in relationship to modifying and controlling the delivery of active agents.This book, "Strategies to Modify the Drug Release from Pharmaceutical Systems," emerged with the aim of providing a comprehensive reference on drug delivery and strategies to modify the drug release from dosage forms, covering all main topics in the field. From the earliest dosage forms to modern drug delivery systems has come great development and growth of acquired knowledge. Thus, this textbook addresses principles, systems, applications, and advances in the field. It is principally a textbook and a reference source of strategies to modify the drug release. Moreover, the characterization, mathematical and physicochemical models, applications, and systems are discussed.Some students and researchers may consider this book an excellent starting point to study the field, while others may find it a source of principles, systems, applications, and advances in the field of drug delivery systems addressed in the same book. It is designed for individuals of diverse backgrounds who are interested in the field of drug delivery. The mathematical and physicochemical principles are highlighted and related with the strategies aiming to discuss and understand the drug release and its possible modifications. It is a book involving the principles, systems, mechanisms, and the state of the art in just one volume.The book is divided into six chapters, according to its sixfold purpose: (I) General considerations, (II) Modification of drug release, (III) Classification of therapeutic systems for drug delivery, (IV) Main mechanisms to control the drug release, (V) Mathematical and physicochemical models of drug release, and (VI) Drug delivery systems. Each chapter is devoted to a specific group of concepts and definitions, and contains contributions from established or emerging researchers around the world who have been working in this field.Through many years of studying and lecturing on this theme for undergraduate and graduate students, I have observed the need to have in one book the discussion about the main strategies to modify the drug delivery and the fundamentals about the theme. I sincerely hope that this textbook will help pharmaceutical students and scientists to understand the fundamentals and main points involving the strategies to modify the drug release. The knowledge about drug delivery systems will enable a more specialized understanding, research and development of drug delivery systems, contributing to patient compliance and enhanced therapy. viii Preface

Drug actions can be improved by developing new drug delivery systems, such as the mucoadhesive system. These systems remain in close contact with the absorption tissue, the mucous membrane, releasing the drug at the action site leading to a bioavailability increase and both local and systemic effects. Mucoadhesion is currently explained by six theories: electronic, adsorption, wettability, diffusion, fracture and mechanical. Several in vitro and in vivo methodologies are proposed for studying its mechanisms. However, mucoadhesion is not yet well understood. The aim of this study was to review the mechanisms and theories involved in mucoadhesion, as well as to describe the most-used methodologies and polymers in mucoadhesive drug delivery systems.Uniterms: Mucoadhesion. Bioadhesion. Mucoadhesive systems. Drugs/delivery. O efeito de fármacos pode ser potencializado através do desenvolvimento de novos sistemas de liberação como os sistemas mucoadesivos. Estes sistemas permanecem em contato íntimo com o tecido de absorção, as mucosas, liberando o fármaco no local de ação, com o consequente aumento da biodisponibilidade, podendo promover efeitos locais e sistêmicos. A mucoadesão, atualmente, é explicada por seis teorias, a eletrônica, da adsorção, da molhabilidade, da difusão, da fratura e a mecânica. Para estudar seus mecanismos e quantificá-la, são propostas várias metodologias in vitro e in vivo. Porém, a mucoadesão ainda não é totalmente compreendida. Esse trabalho tem por objetivo revisar os mecanismos e as teorias envolvidas na mucoadesão, além de descrever as metodologias e os polímeros mais utilizados em sistemas mucoadesivos para liberação de fármacos.Unitermos: Mucoadesão. Bioadesão. Sistemas mucoadesivos. Fármacos/liberação.

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We provide a review of several vaginal mucoadhesive DDS currently in developmental stages or available in the market, immunization via the vagina and special emphasis on the challenges and difficulties associated with delivery of drugs via the vaginal route.