Drug passive targeting

Table 1 Requirements to Achieve Therapeutically Efficacious Passive Targeting of Liposomes Loaded with Drugs and Their Solution...

Polymeric micelles are mostly small (10-100 nm) in size and dmgs can be incorporated by chemical conjugation or physical entrapment. For efficient delivery activity, they shonld maintain their integrity for a sufficient amount of time after injection into the body. Most of the experience with polymeric micelles has been obtained in the field of passive targeting of anticancer drugs to tumours [33]. Attachment of antibodies or sugars, or introduction of a polymer sensitive to variation in temperature or pH has also been stndied [32]. 

Yokoyama, M. 1998. Novel passive targetable drug delivery with polymeric micellSotelated Polymers and Gels, T. Okano Ed., Academic Press, San Diego, pp. 193-229. 

The term blood-brain barrier (BBB) refers to the special obstacle that drugs encounter when trying to enter the brain from the circulatory system. The difference between the brain and other tissues and organs is that the capillaries in the brain do not have pores for the free flow of small molecules in the interstitial fluid of the brain. To enter the interstitial fluid, all molecules must cross a membrane. This design is a protective measure to defend the brain from unwanted and potentially hazardous xenobiotics. Traditionally, drugs that target the brain or central nervous system (CNS) cross the BBB by passive diffusion. Transport by carrier proteins across the BBB is becoming better understood but remains an area of active research. 

Conventional liposomes are those that do not carry any sterically stabilizing or targeting moieties on their surface. Their biodistribution depends strongly on their physicochemical properties (size, potential, composition) and physiological and pathological conditions of the body [193], Thus, conventional liposomes comprise the passive targeting of drug molecules. 

Tumor-targeted drug delivery systems can be classified based on three major approaches (i) passive targeting (ii) active targeting (Fig. 1) and (iii) external stimuli triggering. The advantages and challenges of each approach are discussed below. 

However, the administration of free doxorubicin often leads to dose-limiting side effects such as cardiotoxicity and myelosu-pression. This toxicity can be reduced by liposomal encapsulation of doxorubicin because of the modified biodistribution of the drug (1). Additionally, the efficiency of the drug is improved due to the passive targeting effect of liposomes. 

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