Our case presentation of a patient with acute renal failure caused by dehydration and concomitant medication with negative vasomotor effect on renal haemodynamics reflects one of the chief problems in patients with vascular nephropathy. Such patients are at increased risk of acute deterioration of the pre-existing chronic renal dysfunction as their glomerular filtration rate is dependent on vasoactive agents such as angiotenzin II (AG II) and prostaglandins.