Targeted drug delivery systems are designed to maximize therapeutic response by delivering drug selectively to its pharmacological site(s). There are several factors that determine the availability of drug at the target site. These include the rate of (a) input of targeted drug into the body plasma, (b) distribution of targeted drug to the active site, (c) release of active drug from the targeted drug at the site of action, (d) removal (elimination) of targeted drug and free drug from the target site, (e) diffusion or transport of targeted drug and free drug from the active site to non-target sites, and (f) blood and lymph flow to and from the target site.
APPROACHES TO TARGETED DRUG DELIVERY SYSTEM:
A) Pro-drug :
A prodrug is pharmacologically inert form of an active drug that must undergo transformation to the parent compound in vivo by either chemical or an enzymatic reaction to exert its therapeutic effects.
B) Drug Carrier Delivery System:
Drug-carrier delivery systems employ biologically inert macromolecules to direct a drug to its target site in the body. These are divided into two types: Particulate and soluble macromolecular. Depending on the carrier system, the drug can either be molecularly entrapped within the carrier matrix or covalently linked to the carrier molecules. The major advantage of drug-carrier delivery systems is that the distribution of drug in the body depends on the physiochemical properties of the carrier not those or by alterations in the physiochemical properties of the carrier. There are however several other factors that must be considered in the pharmaceutical development and clinical use of both soluble macromolecular and particulate bio-technical and synthetic site-specific systems.