All Routes Lead to Enhancement

The paucity of new chemical entities and increasing regulatory demands for safety have made drug-delivery improvements essential to drug-product design. In the preface to Enhancement in Drug Delivery, the editors state that "extensive literature [is] available on drug-delivery development and enhancement, however, it is fragmented into specific routes of administration, making it difficult to gain an integrated knowledge in this field." This problem is exactly why this text is timely and immensely needed to overcome the disadvantages of traditional administration.

Gurvinder Singh

The book comprehensively reviews the basics of drug absorption and methods for delivery enhancement through various routes of administration. Its eight parts address oral, rectal, buccal, transdermal, nasal, vaginal, ocular, and central nervous system (CNS) drug delivery. Each part contains chapters that describe the anatomy and basic biopharmaceutics for each route and strategies to enhance drug delivery. The chapters are written by 60 eminent contributors from around the world. Besides discussing their achievements in their areas of expertise, the contributors describe the drawbacks of various enhancers, review current and future approaches to enhancement, and list applications that might inspire new ideas for choosing the ideal promoter for a new application.

The opening chapters provide an in-depth review of gastrointestinal anatomy, physiology, and permeation pathways and discuss enhancers such as surfactants, chitosan, and its derivatives. The role of enzyme inhibitors and secretory-transporter mechanisms also are reviewed. These chapters include examples, toxicities, and formulative approaches to improving the oral-drug bioavailability of lipophilic drugs. Chapters two and three discuss rectal and buccal and sublingual absorption, respectively, and analyze the effect of dosage forms and formulation approaches for these routes of delivery.

Enhancement in Drug Delivery, Elka Touitou and Brian W. Barry, Eds., CRC Press, Taylor & Francis Group, Boca Raton, FL, 2007, 633 pp., ISBN 0-8493-3203-6

Eight chapters are devoted to transdermal delivery, starting with an in-depth description of the stratum corneum. The widest range of enhancement methods being investigated are for transdermal administration. Individual chapters review chemical, iontophoresis, electroporation, ultrasound, and combined methods of enhancement. By way of illustration, the book's discussion of peptide delivery includes the physiological factors affecting nasal delivery, examples of formulations, and challenges for nasal delivery of peptide drugs.

Vaginal drug absorption with chemical enhancers and strategies for improving bioavailability are also presented. Options for expanding ophthalmic pharmaceuticals and developing optimal drug carriers or systems to arrive at the eye are discussed. Lastly, a constructive evaluation of the most significant developments in CNS drug delivery and various strategies to overcome the blood–brain barrier were reviewed.

The editors provide a basic review of the theory behind various administration routes. This review is necessary to appreciate the permeation pathways, enzymes, and secretory-transport mechanisms required for drug delivery. Each chapter has subsections that provide detail, illustrative tables and figures, and references from the scientific literature. A chapter about the combination of drugs in drug delivery, however, would have helped clarify the roles of some drugs as enhancers.

Overall, Enhancement in Drug Delivery is an indispensable resource for pharmaceutical scientists. Its breadth of coverage introduces the subject to those new to the field, and its depth can benefit experienced scientists. The text could form the basis for graduate and postgraduate work in pharmaceutics, medicine, and health-related disciplines. The book is strongly recommended to libraries at universities and pharmaceutical companies.

Gurvinder Singh Rekhi, PhD, is a director of research and development at Elan Drug Delivery, Inc., 1300 Gould Dr., Gainesville, GA 30504, tel. 770.538.6321, gsingh.rekhi@elan.com.