Physical aging of progesterone-loaded poly(D,L,-lactide-co-glycolide) microspheres

Purpose. To study the interactions between a polymeric matrix and a drug during storage at a temperature lower than the glass transition temperature of the polymers. Methods. Poly(lactide-co-glycolide) microspheres loaded with different progesterone ratios were stored at 4, 20 and 40 degrees C. DSC-scans were recorded at regular intervals, depending on the storage temperature. Results. The physical aging of the polymeric matrix, as monitored by the amplitude of the endotherm associated with the glass transition, is slowed down by crystalline progesterone. The development of the progesterone polymorphic depends on the interface/volume ratio of the crystals. Conclusions. For polymeric drug delivery systems, the determination of all studies parameters must take into account an effect of dispersed drugs which are more sensitive as the storage temperature is lower than the glass transition temperature of the matrix.