Protein and peptide drugs hold great promise as therapeutic agents. But there 
are shortcomings: Many recombinant proteins are quickly degraded by proteolytic 
enzymes or are rapidly cleared by kidney filtration resulting in a short 
circulating half-life. Additionally they are prone to be recognized by the 
immune system resulting in the generation of neutralizing and non-neutralizing 
antibodies. PEGylation, a process by which polyethylene glycol chains are 
attached to protein and peptide drugs, can overcome these and other 
shortcomings. By increasing the molecular mass of proteins and peptides and 
shielding them from proteolytic enzymes, PEGylation primarily improves 
pharmacokinetics and helps to prevent adverse drug reactions.