Sustained release system for highly water-soluble radiosensitizer drug etanidazole: irradiation and degradation studies

Etanidazole (one nitro-imidazole hypoxic radiosensitizer) is formulated as polymer matrix type controlled release devices in this study. A novel double polymer drug carrier, unlike the double wall microparticles, is fabricated for the purpose of drug delivery, with the following objectives in mind: (1) to have a high encapsulation efficiency, (2) to achieve a pusatile release profile suitable for the radiation schedule of radiotherapy, (3) to elucidate the degradation profile of these microparticles. Irradiation of the microparticles were also studied to investigate effects on release and degradation. At a dosage of 50 Gy (total dosage during a radiotherapy treatment period) showed no apparent effects on the tri-phase release profile. It consists of an initial burst in the first 72 h, followed by a slow and steady drug release phase, and finally a faster degradation controlled phase corresponding to the degradation state of the different microparticles. At 25 kGy (sterilization dosage), the release profiles of the drug carrier were drastically modified. The faster erosion of the polymer with high dosage irradiation hastened the drug release and shortened the release time span, accompanied by decreases in the polymer molecular weight and glass transition temperatures, which was not apparent from SEM imaging. Degradation studies suggested a heterogeneous degradation process, with the outer layer and inner matrix degrading at different rates. The modifiable tri-phase release profile using microparticles of different polymer blends implies that the release properties of the drug carriers can be modified for different treatment regimes.