Stabilizing Agents for Drug Nanocrystals: Effect on Bioavailability

The objective of this article is to review the spectrum of mathematical models that have been developed to describe drug release from hydroxypropyl methylcellulose (HPMC)-based pharmaceutical devices. The major advantages of these models are: (i) the elucidation of the underlying mass transport mechanisms; and (ii) the possibility to predict the effect of the device design parameters (e.g., shape, size and composition of HPMC-based matrix tablets) on the resulting drug release rate, thus facilitating the development of new pharmaceutical products. Simple empirical or semi-empirical models such as the classical Higuchi equation and the so-called power law, as well as more complex mechanistic theories that consider diffusion, swelling and dissolution processes simultaneously are presented, and their advantages and limitations are discussed. Various examples of practical applications to experimental drug release data are given. The choice of the appropriate mathematical model when developing new pharmaceutical products or elucidating drug release mechanisms strongly depends on the desired or required predictive ability and accuracy of the model. In many cases, the use of a simple empirical or semi-empirical model is fully sufficient. However, when reliable, detailed information are required, more complex, mechanistic theories must be applied. The present article is a comprehensive review of the current state of the art of mathematical modeling drug release from HPMC-based delivery systems and discusses the crucial points of the most important theories.

In the present update on mucoadhesive ocular dosage forms, the tremendous advances in the biochemistry of mucins, the development of new polymers, the use of drug complexes and other technological advances are discussed. This review focusses on recent literature regarding mucoadhesive liquid (viscous solutions, particulate systems), semi-solid (hydrogel, in situ gelling system) and solid dosage forms, with special attention to in vivo studies. Gel-forming minitablets and inserts made of thiomers show an interesting potential for future applications in the treatment of ocular diseases.

D-α-Tocopheryl polyethylene glycol 1000 succinate (simply TPGS or Vitamin E TPGS) is formed by the esterification of Vitamin E succinate with polyethylene glycol 1000. As novel nonionic surfactant, it exhibits amphipathic properties and can form stable micelles in aqueous vehicles at concentration as low as 0.02 wt%. It has been widely investigated for its emulsifying, dispersing, gelling, and solubilizing effects on poorly water-soluble drugs. It can also act as a P-glycoprotein (P-gp) inhibitor and has been served as an excipient for overcoming multidrug resistance (MDR) and for increasing the oral bioavailability of many anticancer drugs. Since TPGS has been approved by FDA as a safe pharmaceutic adjuvant, many TPGS-based drug delivery systems (DDS) have been developed. In this review, we discuss TPGS properties as a P-gp inhibitor, solubilizer/absorption and permeation enhancer in drug delivery and TPGS-related formulations such as nanocrystals, nanosuspensions, tablets/solid dispersions, adjuvant in vaccine systems, nutrition supplement, plasticizer of film, anticancer reagent and so on. This review will greatly impact and bring out new insights in the use of TPGS in DDS. Copyright © 2013 Elsevier B.V. All rights reserved.