Excipient (pharmacologically inactive substance)

What is it?

Polyethylene glycol, referred to as PEG, is used as an inactive ingredient in the pharmaceutical industry as a solvent, plasticizer, surfactant, ointment and suppository base, and tablet and capsule lubricant. PEG has low toxicity with absorption into the body less than 0.5%.

PEGylation occurs when PEGs are attached to various protein medications, allowing for greater solubility for certain drugs. Examples of PEGylated medications include PEG-interferon alpha (Pegintron) and PEG-filgrastim (Neulasta). PEG is also available as a bowel prep for colonoscopy procedures and as a laxative.^[1]

PEG "400" indicates that the average molecular weight of the specific PEG is 400.^[2] PEG 3350 is a laxative available over-the-counter by the name of Miralax. In this case, PEG is considered an "active" ingredient, even though systemic absorption is less than 0.5%.^[2]