Table 4.

Enzyme inhibitors, their targets and effects on peptide delivery. An overview of potentially clinically relevant enzyme inhibitors.

Enzyme inhibitor	Molecules inhibited	Effect on peptide drugs	Ref.
Soybean trypsin inhibitor, FK-448	Chymotrypsin	Enhanced intestinal absorption of insulin in rats and dogs. Suppressed digestion of insulin by pancreatic enzymes	[57]
Aprotinin	Serine proteases, specifically trypsin, chymotrypsin, and plasmin	Intraileally administered insulin with aprotinin led to decrease in blood glucose of 30% compared with controls	[58]
Puromycin	Serine and metallopeptidases	Improved stability of leucine encephalin, and stability and permeability of d-Ala2, d-Leu5 enkephalin (DADLE)	[66–68]
N-acetylcysteine	Inhibits aminopeptidase N and has mucolytic properties		[65,69]
Bacitracin	Trypsin and pepsin, aminopeptidase N	Used to increase delivery of insulin, met-kephamid and buserelin	[65,69,70]