The effect of inorganic salt type and concentration on hydrophilic drug loading into microspheres using the emulsion/solvent diffusion method

Abstract Aim: In order to avoid gastric irritation caused by tolmetin sodium (TS), gastro resistant Eudragit® S 100 microsphere formulations were prepared with the emulsion/solvent diffusion method. Materials: Considering the high water solubility of the TS molecule, the effects of the presence of inorganic salt (NaCl, NaBr and KH2PO4; 0.1 M and 1.0 M) in external phase and external phase pH on the encapsulation efficiency were evaluated. Results: Percentage yield value was found to vary between 55.8% and 72.1%. Improvement in encapsulation efficiency was determined by increasing concentrations of NaCl, NaBr and KH2PO4. The microspheres were observed to have a spherical shape and the measured particle size values varied between 52.1 and 81.5 µm. The released amounts of the drug were found to be low as the inorganic salt concentrations increased. Conclusion: Conclusively, drug release in stomach pH was significantly prevented by the microspheres prepared using Eudragit® S 100 polymer, and these formulations are considered to be a model for other orally administered drugs with similar problems.