bowel diseases, and toxic megacolon. The doses of macrogol as an excipient are too low to have relevant contraindications. Allergy to macrogol is rare, and usually appears as an allergy to an increasing number of seemingly unrelated products, including cosmetics, drugs that use it as an excipient, and peri-procedural substances such as ultrasound gel. Adverse effects Oral macrogol is generally well tolerated. Possible side effects include headache, bloating, nausea, allergies, and electrolyte imbalance, mainly hypokalaemia (low blood potassium levels) and hyperkalaemia (high blood potassium levels). Hyperkalaemia is not an effect of macrogol itself but of potassium salts which are usually part of macrogol formulations. With excessive use, it can cause diarrhea. Interactions The interaction potential is low. Absorption of other pharmaceutical drugs can be reduced because oral macrogol accelerates intestinal passage, but this is seldom clinically relevant. For antiepileptic drugs, such a mechanism has been described in rare cases. Pharmacology Mechanism of action as a laxative Macrogol is an osmotically acting laxative; that is, an inert substance that passes through the gut without being absorbed into the body. It relieves constipation because it causes water to be retained in the bowel instead of being absorbed into the body. This increases the water content and volume of the stools in the bowel, making them softer and easier to pass, as well as improving gut motility. Chemistry Available forms Macrogol is sold as a non-prescription preparation in the form of powder. When sold for gut cleansing (and as a laxative), it is usually in combination with salts such as sodium bicarbonate, sodium chloride and potassium chloride to help mitigate the possibility of electrolyte imbalance and dehydration. Brand names include SoftLax, Purelax, MiraLax, Laxido, Glycoprep, CosmoCol, Movicol, Cololyt, Osmolax, and others. It is dissolved in water to create a clear and odorless solution which is then drunk. While most consumers find the taste of macrogol itself to be very mild and unobjectionable, the electrolytes contained in formulations for purging and cleansing give the solution an extremely salty and bitter taste. Polyethylene glycol-electrolyte solution is a prescription product sold under various brand names including Colyte, Gavilyte, Golytely, Nulytely, Moviprep, and Trilyte. Research PEGylation When attached to various biopharmaceutical medications (which are proteins), macrogol results in a slowed clearance of the carried protein from the blood. This makes for a longer-acting medicinal effect and reduces toxicity, and it allows for longer dosing intervals. It also