Ethylene Glycol Toxicity

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Introduction

Ethylene Glycol is a sweet tasting fluid that is the main constituent of anti-freeze products.[1]. Consequently in northern hemishpere ethylene glycol toxicity is frequently encountered in practice. It has a relatively low minimum lethal dose, and its sweet, palatable taste makes it attractive to dogs, cats and other small animals. [1], [2],[3]


Signalment

  • Dogs: all ages, both sexes, following intoxication lower incidence of fatalities in dogs compared to cats [1]
  • Cats: all ages, both sexes
  • Birds:
  • Other: including pigs and cattle [1]

Diagnosis

Clinical Signs

Severity of clinicals signs is inversely proportional to amount ingested. Time post-ingestion is also important.[3].

  • Dogs: Ataxia, mild to severe increasing depression and other neurological signs, tachycardia, tachypnoea, polydypsia, polyuria, dehydration, anorexia, emesis, miosis, hypothermia
    • if untreated coma and death, or if lesser amount ingested oliguric acute renal failure within 2 to 7 days after ingestion .[3], [1].
      • if untreated anuric acute renal failure
  • Cats: Ataxia, pronounced depression and other neurological signs, tachycardia, tachypnoea, polyuria, dehydration, anorexia, emesis, miosis [1],

[1].

    • coma and death if untreated, or if lesser amount ingested oliguric acute renal failure within 1 day after ingestion
      • if untreated anuric acute renal failure


Laboratory Tests

  • Blood:Metabolic Acidosis, increased serum osmolality, increased anion gap, decreased plasma bicarbonate concentration, decreased PCO2, decrease blood pH
  • Urine:increased urea and creatinine, hyperkalaemia, calcium oxalate crystalluria [3].
  • Hyperphosphataemia due to acute renal failure [3].
    • Hypocalcaemia as a consequence of this[3].

Ultrasonography

  • Renal accumulation of calcium oxalate crystals results in hyperechogenicity upon ultrasound examination [4].

Biopsy

  • Needle or surgical wedge biopsy of kidney [5].

Pathology

Ethylene glycol toxicosis usually results from ingestion although there have been reports of skin contamination resulting in toxicosis in cats [3]. It is absorbed relatively quickly from the gastrointestinal tract [3], hence the quick manifestation of clinical signs following intoxication. After absorption transformation to its more toxic metabolites takes place in the liver and kidney [3]. It is these substances, rather than ethylene glycol itself that are responsible for the more severe pathological changes in the body [3] . The enzyme alcohol dehydrogenase, which is inhibited by 4-methylpyrazole [1] , is responsible for the initial conversion of ethylene glycol to glycoaldehyde [3]. Glycoaldehyde in turn is metabolised to glycolic acid. Following this glycolic acid is converted to glyoxylic acid. This reaction, along with the earlier conversion of ethylene glycol to glycoaldehyde, are the rate-limiting steps in the metabolism of ethylene glycol. Finally glycolic acid undergoes metabolic transformation to produce the end product, oxalic acid. Glycolic acid and oxalate are directly nephrotoxic, leading to necrosis of the renal tubules. Glycolic acid is the main metabolite reposponsible for the metabolic acidosis, although oxalate contributes, as does lactic acid, whose formation is increased as an indirect result of the metabolic pathway outlined above [3] . The metabolic acidosis interferes with normal metabolic pathways [3]. In addition to being directly nephrotoxic oxalate binds ionised calcium in the serum forming calcium oxalate crystals which are excreted by the kidney [3]. . Some of these crystals accumulate within the kidney tubules resulting in further nephrotoxicity and decreased or complete prevention of urine production. The hypocalcaemia that is present is due not only to calcium oxalate crystal formation but also to the hyperphosphataemia that results from the acute renal failure. The decreased serum calcium level leads tetany [3].


Treatment

  • Ethanol: useful in both dogs and cats [3]. Recommended intravenous dose for cats is 5ml of 20% ethanol solution per kg body weight every 6 hours for the first 30 hours and then every 8 hours for the next 32 hours [3] .
  • 4-methylpyrazole: fomepizole Initially thought to be effective in dogs only but if given at a higher dose can be effective in cats also [3]. Its advantage over ethanol is that it has less side effects [3] . Like ethanol its mode of action is to inhibit ADH Cite error: Invalid <ref> tag; invalid names, e.g. too many.

Ethylene Glycol is a weak acid. Therefore in order to increase the rate of renal clearance sodium bicarbonate can be administered to dogs. Intravenous administration of sodium bicarbonate at a concentration of 1-2 mmol/kg every 3 to 6 hours achieves sufficient alkalinisation of the urine.[6]

Prognosis

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 The 5-Minute Veterinary Consult, Canine and Feline, Lippencott, Williams and Wilkins Cite error: Invalid <ref> tag; name "multiple" defined multiple times with different content Cite error: Invalid <ref> tag; name "multiple" defined multiple times with different content Cite error: Invalid <ref> tag; name "multiple" defined multiple times with different content Cite error: Invalid <ref> tag; name "multiple" defined multiple times with different content Cite error: Invalid <ref> tag; name "multiple" defined multiple times with different content Cite error: Invalid <ref> tag; name "multiple" defined multiple times with different content Cite error: Invalid <ref> tag; name "multiple" defined multiple times with different content
  2. ↑ Feline Medicine and Therapeutics
  3. ↑ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18 http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/210900.htm, accessed on 31.10.2010 Cite error: Invalid <ref> tag; name "multiples" defined multiple times with different content Cite error: Invalid <ref> tag; name "multiples" defined multiple times with different content Cite error: Invalid <ref> tag; name "multiples" defined multiple times with different content Cite error: Invalid <ref> tag; name "multiples" defined multiple times with different content Cite error: Invalid <ref> tag; name "multiples" defined multiple times with different content Cite error: Invalid <ref> tag; name "multiples" defined multiple times with different content Cite error: Invalid <ref> tag; name "multiples" defined multiple times with different content Cite error: Invalid <ref> tag; name "multiples" defined multiple times with different content Cite error: Invalid <ref> tag; name "multiples" defined multiple times with different content Cite error: Invalid <ref> tag; name "multiples" defined multiple times with different content Cite error: Invalid <ref> tag; name "multiples" defined multiple times with different content Cite error: Invalid <ref> tag; name "multiples" defined multiple times with different content Cite error: Invalid <ref> tag; name "multiples" defined multiple times with different content Cite error: Invalid <ref> tag; name "multiples" defined multiple times with different content Cite error: Invalid <ref> tag; name "multiples" defined multiple times with different content Cite error: Invalid <ref> tag; name "multiples" defined multiple times with different content
  4. ↑ Textbook of Veterinary Internal Medicine, (Seventh Edition), Ettinger and Feldman; p1968
  5. ↑ Textbook of Veterinary Internal Medicine, (Seventh Edition), Ettinger and Feldman; p1968
  6. ↑ Canine Medicine and Therapeutics (Fourth Edition, 1998),Blackwell Science, p1049
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