Patients with known chronic renal insufficiency. [As all cholera patients with moderate to severe dehydration have pre-renal insufficiency on admission, and as it is not possible to detect whether a patient has renal failure until the patient has been hydrated for at least 24 hours, serum creatinine will be checked 24 hours post-administration of first dose of study medication, on Day 5, and at any time as clinically indicated. (If the baseline creatinine is > 200 mcmol/L, any patient with creatinine > than 200 mcmol/L 24 hours post-administration, will be considered as suffering from renal failure and will be withdrawn from the trial.) Patients with known cardiac or hepatic impairment, i.e. SGOT/SGPT or bilirubin > 3 times the upper limit of normal, and patients with a history of central nervous system (CNS) disorders (known risk of experiencing seizures, a history of convulsive disorders or head injury trauma, currently on anti-seizure medication or within two months post-stroke).