Ethylene Glycol Toxicity in Small Animals

Introduction

Ethylene glycol toxicity is one of the most critical toxicologic emergencies in small animal practice, due to the potential for severe metabolic and renal effects if not treated promptly. The sweet taste of ethylene glycol contributes to accidental ingestion by dogs and cats, particularly in household environments where automotive products are present.¹ However, early intervention can markedly improve survival outcomes in these cases.

Pathophysiology

Ethylene glycol itself has limited inherent toxicity. The majority of clinical effects are due to hepatic metabolism via alcohol dehydrogenase (ADH), which converts ethylene glycol into glycolic acid, glyoxylic acid, and ultimately oxalic acid.² Glycolic acid is responsible for the development of severe high anion gap metabolic acidosis, while oxalic acid complexes with calcium to form calcium oxalate crystals, which precipitate within renal tubules, leading to obstruction and acute tubular necrosis.²

Renal damage is the principal cause of mortality and occurs primarily due to calcium oxalate crystal deposition, direct tubular epithelial injury, and severe metabolic acidosis. The minimum toxic dose of ethylene glycol is species dependent:

• Dogs: approximately 4–6 mL/kg of concentrated antifreeze
• Cats: approximately 1.4 mL/kg¹

Cats appear to be more sensitive due to rapid metabolism and their narrow therapeutic window.¹

Clinical Presentation

Ethylene glycol toxicity typically progresses through three clinical stages:

Stage 1 (0–12 hours): Central nervous system depression, ataxia, vomiting, and polyuria/polydipsia. Signs may resemble ethanol intoxication.²

Stage 2 (12–24 hours): Transient improvement in neurologic signs may occur, while metabolic acidosis worsens. Tachycardia, tachypnea, and dehydration are common.²

Stage 3 (24–72+ hours): Acute renal failure develops, characterized by azotemia, hyperphosphatemia, hyperkalemia, and progression to oliguria or anuria.¹

Diagnostic Evaluation

Diagnosis is based on history, clinical presentation, and laboratory findings. Early laboratory abnormalities include high anion gap metabolic acidosis and decreased bicarbonate concentration. An increased osmole gap may be present prior to full metabolism of ethylene glycol.² As renal injury progresses, azotemia, electrolyte abnormalities, and possible hypocalcemia develop.¹ Urinalysis may reveal calcium oxalate monohydrate crystals, which strongly support the diagnosis in the appropriate clinical context.³

In-house ethylene glycol assays detect unmetabolized compound and are most reliable within the first several hours after ingestion. Sensitivity declines as metabolism proceeds.¹

Treatment

Treatment success depends primarily on time to intervention. The primary therapeutic objective is inhibition of alcohol dehydrogenase to prevent formation of toxic metabolites.

Fomepizole is a competitive ADH inhibitor and is considered the treatment of choice when available, due to its safety and predictable pharmacokinetics.¹

Ethanol is an effective alternative but requires intensive monitoring because of risks including CNS depression and hypoglycemia.³

Supportive care includes aggressive intravenous fluid therapy, correction of acid-base and electrolyte disturbances, and close monitoring of urine output and renal parameters.¹ In advanced cases with severe azotemia or anuria, hemodialysis may be required to remove toxins and support renal function.²

Prognosis and Prevention

Prognosis is highly time dependent. Dogs treated within approximately five hours of ingestion often recover fully.¹ Cats must be treated even earlier. Once azotemia develops, prognosis declines significantly.¹ Anuric renal failure carries a grave prognosis in the absence of dialysis.²

Client education is essential. Safe storage of antifreeze products and prompt cleanup of spills can significantly reduce exposure risk. Propylene glycol–based antifreeze products are less nephrotoxic alternatives, though not entirely benign.¹

Key Take-Home Points

• Ethylene glycol toxicity is a true medical emergency.
• Toxicity results from metabolism to glycolic and oxalic acids.
• Early metabolic acidosis precedes renal failure.
• Alcohol dehydrogenase inhibition is the cornerstone of therapy.
• Time to treatment is the most important prognostic factor.

Prompt recognition and rapid intervention can mean the difference between complete recovery and irreversible renal failure.

References

1. Peterson, ME, and PA Talcott. “Chapter 47: Ethylene Glycol.” Small Animal Toxicology. 3rd ed. Saunders, 2013: 551-567.
2. Thrall, MA, et al. “Clinicopathologic findings in dogs and cats with ethylene glycol intoxication.” JAVMA. 1984;184 (1): 37-41.
3. Kraut, Jeffrey A., and Michael E. Mullins. “Toxic Alcohols.” New England Journal of Medicine. 2018; 378 (3): 270–80.