Several toxic alcohols are of medical and toxicological importance; the principal ones include ethanol, ethylene glycol (EG), methanol, and isopropanol. See Alcohol Toxicity. This article discusses ethylene glycol, which is extremely toxic. If untreated, ingestion of ethylene glycol can be fatal.
Ethylene glycol is the major ingredient of almost all radiator fluid products in the United States. It is used to increase the boiling point and decrease the freezing point of radiator fluid, which circulates through the automotive radiator. These changes to the boiling and freezing points result from the colligative properties of the solute (ie, they depend on the number of particles in the solution). Hence, ethylene glycol is added to prevent the radiator from overheating or freezing, depending on the season.
Fluorescein dye is often added to radiator fluid to help mechanics identify the source of a radiator leak. The fluorescein in the fluid fluoresces when viewed under ultraviolet light.
Ethylene glycol tastes sweet, which is why some animals are attracted to it. Many veterinarians are familiar with ethylene glycol toxicity because of the frequent cases that involve dogs or cats that drink radiator fluid.
Initially, patients with ethylene glycol intoxication may be asymptomatic; with time they will develop altered mental status and dyspnea. The classic laboratory profile is an early osmolar gap that later transitions to an anion gap metabolic acidosis. Initial treatment includes infusion of crystalloids to enhance renal clearance of the toxic metabolites. Ethyl alcohol has traditionally been used for antidotal treatment, but it has largely been supplanted by fomepizole.
Like the other toxic alcohols mentioned above (see Background), ethylene glycol is a parent compound that exerts most of its toxicity by conversion to metabolites. Ethylene glycol itself may cause some alteration of mental status but it is a relatively nontoxic compound before it is metabolized. The metabolites cause the distinctive toxicity associated with this compound.
Knowing the pathway of ethanol metabolism is necessary to understand ethylene glycol toxicity properly. Ethanol is metabolized by the enzyme alcohol dehydrogenase (ADH) pathway, which is located in the liver and gastric mucosa, and by the cytochrome P-450 mixed function oxidase (MFO) system in the liver. The mixed function oxidase component is subject to greater inducibility than alcohol dehydrogenase.
As with ethyl alcohol and methanol, ethylene glycol is metabolized by the enzyme alcohol dehydrogenase. In this step it forms glycoaldehyde. Through interaction with aldehyde dehydrogenase, ethylene glycol is then metabolized to glycolic acid (GA). A profound acidosis often ensues with this intoxication which is attributable to the glycolic acid in circulation. This glycolate is then transformed into glyoxylic acid. At this point, the molecule may be transformed into the highly toxic oxalate or the safer glutamate or α-ketoadipic acid metabolites.
Calcium oxalate crystals may form and accumulate in blood and other tissues. The precipitation of calcium oxalate in the renal cortex results in decreased glomerular filtration and renal insufficiency. The formation of these crystals consumes circulating calcium, and hypocalcemia may occur.
The rate-limiting step of ethylene glycol metabolism is the alcohol dehydrogenase–catalyzed step. Common ethyl alcohol (ethanol) binds much more easily to alcohol dehydrogenase than ethylene glycol or methanol does. Because ethanol is the preferred substrate for alcohol dehydrogenase, the presence of ethanol may essentially block metabolism of ethylene glycol. In addition, this enzyme is blocked by the administration of fomepizole (4-methylpyrazole [4-MP]), which is discussed below (see Emergency Department Care). This is the basis of one therapy used in the United States.
Upon oral ingestion, serum levels of ethylene glycol peak within 1-4 hours. The elimination half-life (assuming preserved renal function) is 3 hours.
Ethylene glycol is a relatively common cause of overdose in US emergency departments. In 2009, there were 5282 single exposures to ethylene glycol reported to the American Association of Poison Control Centers (AAPCC).  In 20142, the number of single exposures to ethylene glycol in antifreeze and other automotive products had increased to 5552. 
According to the AAPCC's National Poison Data System, in 2009, 773 had minor outcomes, 376 had moderate outcomes, 134 had severe outcomes, and 10 deaths were documented.  In 2014, 916 had minor outcomes, 411 had moderate outcomes, 141 had severe outcomes, and 16 deaths were documented. 
The annual report of the AAAPCC's National Poison Data System in 2014 documented ethylene glycol exposure in 432 children younger than 6 years, 560 in those aged 6-19 years, and 3942 in those 20 years and older. 
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