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Sustained release mini-matrices (multiple unit dosage form) were developed by means of hot-melt extrusion using ibuprofen as the model drug and ethyl cellulose as sustained release agent. Ibuprofen release from the ibuprofen–ethyl cellulose matrices (60:40 w/w) was too slow (20% in 24 h). Other excipientia (hydroxypropyl methylcellulose and xanthan gum) were added to the formulation to increase the drug release. Changing the viscosity and substitution type of HPMC, the amount of HPMC, the drug load and the HPMC:EC ratio modified the in vitro drug release. Burst release was noticed for the formulations containing HPMC and a nearly time independent drug release was seen for the xanthan gum based mini-matrices. Drug release from the mini-matrices was mainly diffusion controlled and swelling played an important role to obtain complete drug release. The formulations were at least 12 months stable during storage at 60% RH and room temperature. At a higher relative humidity and temperature the drug release increased.