Some colonoscopy preps require drinking up to a gallon of liquid, while many newer preps allow for split dosing. Common colonoscopy preps include polyethylene glycol, oral sodium phosphate solution, oral sodium phosphate tablets and magnesium citrate, reports Harvard Medical School.
Polyethylene glycol is often marketed under brand names such as Golytely and Miralax. Polyethylene glycol may involve split dosing, and generally 1 gallon of the fluid is ingested in 8-ounce increments. In addition to having a salty taste that may be unpleasant, the volume of fluid contained in this prep may cause nausea or vomiting, explains Harvard Medical School.
Oral sodium phosphate is a prep that may be prescribed as a solution under brand names such as Fleet Phosphosoda EZ-Prep or as tablets under brand names such as Visicol or OsmoPrep. With solutions, two doses are diluted in water and taken 10 to 12 hours apart, and each dose is followed by at least 16 ounces of liquid. With tablets, split dosing also occurs with a total of 20 tablets taken the evening before, and 12 to 20 tablets taken hours prior to the procedure. Side effects of oral sodium phosphate preps include dehydration and electrolyte imbalances, according to Harvard Health Publications.
Many over-the-counter preps contain magnesium citrate. Using split dosing, 15 ounces of magnesium citrate may be ingested the evening before the procedure, and 15 ounces six hours before the colonoscopy. Magnesium citrate is often accompanied by laxatives such as Dulcolax, states Harvard Medical School.