Formulation of Silicone Matrix Systems for Long Term Constant Release of Peptides

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Abstract
Theoretically, release of drug through the water-filled pores of matrix systems is expected to show a square-root-of-time dependence, with time exponents of 0.5 and hence continuosly declining release rates. Yet there have been many research groups finding remarkable deviations. The aim of this work was to investigate on factors which lead to deviations from the square-root-of-time law and may be helpful for the development of matrix systems with constant drug release for long time. Matrices of polydimethylsiloxane (PDMS) were prepared incorporating varying amounts of different pore-building, water soluble hydrogels. The hydrophilic model drug was Gly-Tyr. The following essential factors influencing the long-term release profiles were found: (i) total matrix loading, (ii) its dissolution rate and (iii) the viscosity of the pore-building hydrogel. A proper choice of conditions lead to release profiles with time-exponents up to 0.8 for a time period of several weeks.