TIME-DEPENDENT ORAL DELIVERY SYSTEMS FOR COLON TARGETING

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