The oral route constitutes the preferred route for drug delivery. However, numerous drugs remain poorly
available when administered by this route. In order to circumvent this problem, it has been proposed to incorporate drugs
successfully to polymeric nanoparticulate systems containing mucoadhesive polymer(s) because of their propensity to
interact with the mucosal surface. Peptide drugs are poorly absorbable and are also susceptible to enzymatic degradation
in the gastrointestinal tract. In order to overcome physiological and morphological barriers against peptide/poorly
absorbable drug delivery, two possible approaches mucopenetrative and/or mucoadhesive properties for drug carriers have
been considered. Mucoadhesion can prolong the residence time of drug carriers at the absorption sites, improved drug
absorption and controlled drug release from the devices used. The particles with smaller size are likely to diffuse much
higher in the mucus layer, provided that diffusion of the particles in the mucus layer obeys the Stokes–Einstein equation.
The adhesiveness of the nanoparticles (NPs) in suspension form helps to improve bioavailability and also improves
targeting of the parasites persisting in the GIT e.g., Cryptosporidium parvum.
Chitosan (CS) based or CS coated NPs represent another common group of mucoadhesive systems and several groups
have studied NPs made of these polymers for the enhancement of bioavailability and mucoadhesion of proteins, peptides,
and DNA to mucosal tissues. The present review focuses on the gastrointestinal mucoadhesion of NPs for peptide/poorly
absorbable drugs. The use of this mucoadhesive NPs delivery system for peptide/poorly absorbable drugs is one of the
areas that need to be explored in the future.