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1.1 Challenges of conventional drug delivery Traditional drug delivery systems include oral drug administration, injection, infusion, and topical administration, where the drug is applied to body surfaces such as the skin or mucous membranes. Many of the conventional drug delivery systems distribute the pharmaceutical compound proportionally to the regional blood flow through the systemic blood circulation. Consequently, the drug is delivered indiscriminately throughout the whole body to diseased and healthy tissues. As a result, patients suffer from side effects due to the non-specific delivery of the drug. Systemic delivery of a drug with body-wide distribution also results in a limited availability of the therapeutic agent at the site of interest, lowering the ability of the drug to produce a beneficial effect. To compensate for the low availability of the drug at the affected site, the drug has to be administered in large quantities, resulting in increased drug toxicity as well as high therapy costs. Another drawback of systemic drug delivery is the short circulation half-life of many drugs, which leads to the administration of high drug concentrations or high dosing frequencies (Branco & Schneider, 2009). Pain and discomfort caused by frequent drug applications are another challenge of conventional drug delivery, especially for children and the elderly. First steps have been made in the development of micro needle injection and needle-free injection to reduce the pain and inconvenience of injections (Brunner, 2004; Stoeber & Liepmann, 2002). As beneficial as mechanical improvements in drug delivery will be for the patient’s comfort and compliance, they will not reduce the number of administrations or the amount of required therapeutic. They also will not affect drug toxicity or effectiveness. To maximize the therapeutic effect of a drug, the appropriate concentration of the drug has to be available at the right location and time, while sparing healthy tissues. Therefore, new tools are needed that enable the delivery of drugs directly to the diseased area, and/or release the therapeutic agent in a controlled way. In this chapter, vehicles for the targeted delivery of drugs will be discussed, with special focus on the potential use of human mesenchymal stem cells (hMSCs) for targeted therapies. Besides the development of targeted drug delivery tools, efforts in the medical field attempt to increase the efficiency of conventional applications. An example is topical drug delivery, which has profited from the introduction of new topical applications including transdermal patches (Brunner, 2004), use of microneedles (Henry et al., 1998), electroporation techniques |
