Preparation and In Vivo Evaluation of Extended Release Trilayer Matrix Tablets Containing Simvastatin Solid Dispersions

The solid dispersion method was originally used to improve the dissolution properties and the bioavailability of poorly water soluble drugs by dispersing them into water soluble carriers. In addition to the above, dissolution retardation through solid dispersion technique using water insoluble and water swellable polymer for the development of controlled release dosage forms has become a field of interest in recent years.  The objective of this present investigation was to develop extended release (ER) trilayer matrix tablets containing simvastatin solid dispersion prepared by direct compression and consisted of middle active layer with different grades of hydroxypropylmethylcellulose (HPMC), guar gum, ethyl cellulose. Upper and lower layers are prepared with Carnauba wax, guar gum and carbopol 934P. The developed drug delivery system provided prolonged drug release rates over a period of 24 h. The release profile of the optimized formulation (HF14) was described by the Zero-order and Higuchi model. In-vivo bioavailability studies were carried out with the optimized formulation (HF14) and reference standard.  A fair correlation between the dissolution profile and bioavailability for the optimized formulation was observed. The results indicate that the approach used could lead to a successful development of a trilayer extended release formulation up to 24h. These results also demonstrated that the Simvastatin solid dispersion incorporated trilayer tablets shown more bioavailability because of its conversion from crystalline to amorphous form.