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The therapeutic potential of many pharmaceutical proteins would highly benefit from the availability of controlled release systems for the constant or pulsed release of the intact protein. Several potential candidates for controlled release strategies are listed in Table 1. At present, alternative routes of administration to the parenteral route show little promise except for the pulmonary route.
This article focuses on parenteral delivery systems. So, we 'stick to the needle' but use controlled release delivery systems for these proteins: to produce the desired pharmaco-kinetic profile, for example to prevent high initial plasma concentrations (often 'the flatter, the better'); to reduce the injection frequency and improve patient-friendliness of the therapy; and to reduce the necessity of frequent involvement of trained medical personnel.
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A number of strategies have been developed to control the release of proteins as a function of time (1). Proteins have been formulated in amorphous form or as crystals (for example insulin) to ensure release over a short period of up to two days. A second strategy uses a pump with a catheter and fixed needle to administer drugs for local or systemic delivery. These pumps have the advantage of control over pump rate and proven reliability of the technology, but even the miniaturised devices are expensive and become rather bothersome for the patients in the long run. Thirdly, liposomal dispersions release their content over periods of up to three weeks after subcutaneous injection. |
