Patients are excluded if they had known allergy to one of the tested preparations such as bisacodyl (Bisacodyl VP, ICN Polfa, Rzeszow, Poland), polyethylene glycol (Fortrans, Beaufour Ipsen Industry, Dreux, France) and/or sennoside (Xenna Extra, US Pharmacia, Wroclaw, Poland) and had disorders that make oral intake of the preparation impossible (neurological disorders, intestinal obstruction, mental retardation etc.).