Characterization of calcium alginate beads containing structurally similar drugs.

The aim of this study was to investigate the characteristics of alginate beads prepared by ionotropic gelation in which structurally similar drugs were incorporated. For this purpose theophylline and theobromine were selected as model drugs. The influence of incorporated drugs on bead characteristics such as size, shape, and morphology, as well as encapsulation efficiency, was examined. It was found that theobromine as well as theophylline content in beads significantly decreased with increasing hardening time due to drug diffusion into the hardening media. In theobromine beads the drug content was extremely improved by dropping the alginate and drug solution into an acidic calcium chloride solution, while theophylline content was to some extent improved by the hardening of beads in a calcium chloride solution saturated with the drug. The most evident difference between theophylline and theobromine beads was in their shape and morphology. Theobromine beads were round, while theophylline ones had an irregular shape with an extremely wrinkled surface. The distinction in shape was highly dependent on drug content. Additionally, it was demonstrated that beads' shape was dependent on preparation conditions as well. On the basis of x-ray powder diffraction (XRPD) and differential scanning calorimetry (DSC) analyses and scanning electron microscope (SEM) photographs it was found that the most of the drug in bead was present in an amorphous state. Therefore, it is suggested that some drug-alginate interactions could be present in beads and might be responsible for the different shape of theophylline and theobromine beads. Thus it can be concluded that the preparation of beads by ionotropic gelation cannot be generalized even though structurally similar drugs are incorporated.