ABSTRACT
Insult is added to injury if patients with chronic renal impairment are prescribed drugs normally excreted by the kidneys which are nephrotoxic in themselves if high blood levels are attained. A prime example is gentamicin (see Chapter 10). Non-steroidal anti-inflammatory drugs constitute another group of commonly prescribed agents which may superimpose an interstitial nephritis upon an established other cause of chronic renal impairment, thus hastening deterioration in renal function. The risk of contrast nephrotoxicity is increased in patients with renal impairment, especially if the patient is bloodvolume depleted when the contrast is administered. In patients with normal renal function subjected to intravenous urography (see Chapter 1), it is usual to deprive the patient of fluid for some hours before the examination. The aim is to stimulate avid reabsorption of fluid from the renal tubules (which is a natural response to prolonged fluid deprivation) and thus concentrate the contrast medium within the kidney substance, so obtaining better quality imaging of the kidneys and urinary tract. Such fluid deprivation in renal impairment is both futile (because urinary concentrating capacity is impaired) and dangerous (since the risk of contrast nephrotoxicity is greater if the patient is blood-volume depleted).
