Drugs, in the majority of cases, are toxic at high doses however, they must be present in the circulation for a time sufficient to reach therapeutically useful results. This is commonly achieved by repeated drug administrations, which give rise to peak and valley drug concentration. Such a method of administration has two disadvantages: on the one hand the low compliance by the patient and, on the other, the risk of reaching toxic levels. This chance is very severe in particular for new biotechnological drugs such as peptides, proteins, or oligonucleotides that usually are very active and often have a very narrow therapeutic window. A solution to these problems comes now from the drug controlled release technology, meaning with this word also programmable or pulse release from insoluble matrices. The chemical modification of the drug by soluble polymers to increase the residence time in blood, as well as to convey more favorable properties such as the reduction of antigenicity or increased stability toward enzymes, is also considered part of the technology. In any of these cases not only desirable and constant drug levels are reached, but also a release that may last for a long time, up to one year. To reach this goal the drug is usually entrapped when the matrix is produced or shaped, and only in rare cases is it absorbed into the matrix from a concentrated drug solution. The technology described above does not apply only to systemic drug treatment, i.e., distribution through the whole body via the blood, but also sometimes to localization in a particular area, as occurs, for instance, in wound treatment and in medication of inflamed epidermis as well as of eyes,