One of the aims included in the United Nations Millennium Development Goals is to decrease the number of the world’s population without access to sanitation and water that is safe, by half by the year 2015. The use of water that is not safe for consumption leads to water–related diseases. For the purpose of this study gastro–intestinal disease was redefined as diseases of the gastro–intestinal tract caused by pathogens that spread via contaminated drinking water, poor sanitation and inadequate hygiene. Information obtained regarding the use of gastro–intestinal disease medication, may provide information about the prevalence of gastro–intestinal disease in South Africa. The general objective of this study was to determine the prescribing patterns of gastro–intestinal medication in different geographical areas in the private health care sector of South Africa. A retrospective drug utilisation review was conducted on data obtained from a medicine claims database of a pharmacy benefit management company for 2007 and 2008. A pharmacoepidemiological approach was followed in order to determine the prevalence of gastro–intestinal disease as well as the use of gastro–intestinal medication in South Africa as well as the different provinces of South Africa. The impact of water quality and sanitation on the prevalence of gastro–intestinal disease was also investigated. Gastro–intestinal medication (used in the treatment of gastro–intestinal disease) included the following pharmacological groups according to the MIMS®–classification: antivertigo and anti–emetic agents (group 1.8), antispasmodics (group 12.3), antidiarrhoeals (group 12.7), minerals and electrolytes (group 20.4, selected according to specified NAPPI–codes) and antimicrobials (group 18). Antimicrobials had to be prescribed in combination with one of the specified gastro–intestinal medication groups in order to be classified as a gastro–intestinal medication. In 2007 and 2008 respectively, 428864 and 340921 gastro–intestinal medication items were prescribed. The most frequently prescribed gastro–intestinal medication pharmacological groups in 2007 and 2008 were beta–lactam antimicrobials (with proportion percentages of 22.77% and 20.85% in 2007 and 2008 respectively), antivertigo and anti–emetic agents, antispasmodics, antidiarrhoeals and quinolone antimicrobials. Minerals and electrolytes represented only a small proportion (2.99% and 2.56% in 2007 and 2008 respectively) of the prescribed gastro–intestinal medication in South Africa. In the Free State and Western Cape antivertigo and anti–emetic agents were the most frequently prescribed gastro–intestinal medication items, while in other provinces beta–lactam antimicrobials ranked the highest. In all provinces except the Western Cape and the Northern Cape, amoxicillin/clavulanic acid was the most frequently prescribed gastro–intestinal medication active ingredient. In the Western Cape loperamide was the most frequently prescribed active ingredient, while ciprofloxacin ranked highest as active ingredient in the Northern Cape in 2008. Based on the prescribing patterns of gastro–intestinal disease medications the treatment of gastro–intestinal disease in this section of the private health care sector of South Africa, does not fully comply with the Standard Treatment Guidelines with regard to the use of antimicrobials and electrolyte replacement therapy. / Thesis (M.Pharm. (Pharmacy Practice))--North-West University, Potchefstroom Campus, 2011.