The importance of gastrointestinal uptake of particles in the design of oral delivery systems

The oral delivery of drugs and vaccines is regarded as the optimal means for achieving therapeutic and prophylactic effects for a number of conditions. For both drug and vaccine delivery the enteric route has the advantages of increased patient compliance, relieves the need for injection and does not require the presence of trained personnel. In the case of vaccination, enteric delivery may result in the induction of a protective mucosal immune response against pathogens which colonise and invade the mucosae. Unfortunately, the oral delivery route is beset with problems such as: gastrointestinal destruction of labile molecules; low levels of macromolecular absorption; and poor immunity usually elicited to orally applied soluble vaccine antigens. To reduce the impact of gut secretions and to ensure the absorption of bioactive agents in an unaltered form, molecules may be incorporated into biodegradable microparticles. This oral delivery system therefore relies on the capacity of the gastrointestinal tract to absorb microparticulate materials, a function which has been demonstrated to be carried out by membranous/microfold (M) cells in the Peyer's patches of the mammalian gut. This review examines the nature and extent of particulate absorption by the gut and considers the implications of this process for the oral delivery of drugs and vaccines.