Due to their low oral bioavailability, most protein drugs are only ava
ilable as parenteral formulations. The oral delivery of proteins is ch
allenging and has often been considered an unattainable goal; neverthe
less, the efforts to develop oral formulations of proteins continue to
be numerous. The approaches devised to overcome the obstacles for the
absorption of proteins from the gastrointestinal tract are various, a
nd include the co-administration of enzyme inhibitors and/or absorptio
n enhancers, the encapsulation in liposomes, microemulsions, or biodeg
radable particles, and the modification of proteins through the attach
ment of chemical moieties. This article reviews the recent patent lite
rature related to formulation strategies to improve the oral bioavaila
bility of proteins.