Poisons affecting the kidney
Abstract
The kidney has an essential role in maintaining normal physiological functions but it can be affected by various drugs and chemicals. A common seasonal cause of renal failure in cats is ingestion of antifreeze containing ethylene glycol. It is not the ethylene glycol itself which causes renal failure but toxic metabolites which result in deposition of calcium oxalate crystals in the renal tubules. Various non-steroidal anti-inflammatory drugs (NSAIDs), particularly those used in human medicine such as ibuprofen, flurbiprofen and naproxen, cause renal effects through inhibition of prostaglandin synthesis which results in reduced renal blood flow and disruption of normal renal function and homeostatic mechanisms. For some common substances, such as lilies in cats and grapes and their dried fruit in dogs, kidney injury occurs through unknown mechanisms. Management of poison-induced kidney injury is supportive with monitoring and support of renal function. Although haemodialysis and other extracorporeal techniques can be used, they are rarely available in veterinary medicine and therefore preventive measures are used. This includes aggressive intravenous fluid therapy before onset of signs for lily and grape poisoning and early use of the antidote (ethanol) in ethylene glycol poisoning to prevent formation of toxic metabolites, allowing excretion of the parent compound. In most cases, once kidney injury is advanced, prognosis is poor.
The kidney has multiple functions including regulation of extracellular fluid volume, electrolytes and pH, excretion of waste and toxins, and hormone production. In the last article looking at poisons by organ system, we discuss some poisons that affect the kidney. Some substances cause renal damage as a result of toxic metabolites or interference with normal physiological processes; however, for other substances, the mechanism of renal injury is unknown. A few other potential causes of kidney injury in companion animals are given in Box 1.
Box 1.Other potential causes of kidney injury
Grapes and their dried fruits, sultanas, raisins and currants (Figure 1) are found in a variety of foodstuffs and poisoning has occurred after ingestion of the raw fruit (with or without seeds), as well as cooked foods such as fruit cakes (including Christmas cake) and other baked goods. Toxicosis has been reported from grapes grown in the home environment, from wineries and those brought from supermarkets (McKnight, 2005). Grape pomace or marc, which comprises the skins, pulp, seeds and stems of fruit after pressing have also caused renal injury (Lovell and Harvey, 2006).
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