Drug Targeting and Delivery

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Drug delivery is defined as mechanisms to introduce pharmaceutical compounds to human in order to achieve therapeutic effects. We have come a long way since chewing medicinal plants and inhaling soot from medicinal substance were the only form of drug delivery. These approaches lacked consistency and uniformity of drug delivery. Since then there has been a continuous effort to discover and improve drug delivery routes and drug delivery systems. Conventional drug delivery system includes drug delivery via oral route as solutions, suspensions, emulsions, and tablets. Some are delivered systemically via injections and intravenous application. Medications are applied topically as lotions and gels. Nasal route is used for drug delivery to lungs by inhalers and nebulizers. Apart from antibiotics, vaccines, and chemical compounds, modern medicine includes recombinant DNA, insulin, interferon, interleukin, erythropoietin, tissue plasminogen activator, and other peptides and macromolecules as drugs that require efficient drug delivery systems. Traditional drug delivery systems suffer from various limitations such as low bioavailability, intolerance, toxic side effects, reduced plasma half-life, higher concentration, and low efficacy. The hydrophilic drugs have difficulty in passing through the cell membrane. Systemically delivered drugs reach all the organs irrespective of the affected organ. This causes toxic side effects on the healthy cells. The drugs tend to degrade fast in the plasma so higher doses of drug are required and hence it becomes toxic with reduced efficacy and are expensive. The biological barriers exclude the drug from reaching the affected cells and tissues. Efficient drug targeting can improve drug delivery efficacy, reduce side effects, and lower treatment cost. Hence, much effort is given on the development of novel carriers that would meet the requirement of drug delivery systems. The main areas of research are to increase bioavailability of the drugs, increase plasma half-life, and target to specific organs or cells. This would result in lowering the dose, which would also lower drug-induced toxicity, protect bystander cells and organs from adverse side effects, and reduce medical expenses. In this chapter, we will discuss the biological barriers, advances in drug delivery systems, drug targeting, and their application in diseases.