Time-dependent oral delivery systems for colon targeting

A solid oral dosage form consisting of a core coated with two polymeric layers is proposed for colonic specific delivery of drugs. The system, designed to exploit the relatively constant small intestinal transit time, satisfactorily meets the requirements of the so-called time-based positioning drug product design, i.e. resistance to acidic environments, silent phase of predetermined time duration, and rapid release of the active ingredient. The outer layer dissolves at pH > 5 whilst the inner layer provides the delay phase. Aqueous solutions of low-viscosity hydroxypropylmethyl cellulose (HPMC) as a retarding material were used for coating cores containing a tracer substance. Conventional ceasing operations were performed with both fluidized bed and rotating part equipment, giving units with a continuous layer of good technological quality. A fine modulation of lag time was achieved by varying the thickness of the HPMC retarding layer, which works according to a swelling/erosion mechanism. Such time-based positioning systems are intended to transport an intact solid core, addressing, before release can start, specific portions of the intestine, as dictated by intestinal transit time features.