Polyethylene glycol (PEG) is a synthetic polymer that polymerizes ethylene oxide molecules and connects ethylene glycol units through ether bonds. PEG is a water-soluble polymer, and each PEG molecule can form hydrogen bonds with 100 water molecules. The molecular weight of PEG varies with the time of the polymerization process, and the molecular weight represents the weighted average of individual PEG molecules. The physical and chemical properties of PEG vary depending on its molecular weight: when the molecular weight is less than 1000, PEG is a liquid, and as the molecular weight increases, the molecules become waxy solids. The most common PEG formulations include PEG 3350 and PEG 400. PEG has different applications in many fields from medicine to industry. PEG has a long history in gastroenterology: PEG 3350 is a common over-the-counter permeable laxative used to relieve occasional constipation. PEG 3350 is also used to clean the colon and prepare for adult colonoscopy.
The basic principle of using PEG in gastroenterology is due to the physical properties of the compound: its strong water binding capacity, negligible intestinal absorption with the increase of molecular weight, no significant toxicity, and limited intestinal enzymatic degradation or bacterial metabolism make PEG a useful therapeutic agent for treating sporadic constipation and preparing for colonoscopy.