Ethylene glycol (HO—CH₂—CH₂—OH) is a major component of antifreeze. If ingested, it is first converted to HOOC—CHO (oxoethanoic acid) and then to HOOC—COOH (oxalic acid), which is toxic.
<IMAGE>
b. The treatment for the ingestion of ethylene glycol is an intravenous solution of ethanol. How might this help prevent toxic levels of oxalic acid in the body?

Verified step by step guidance

1. Understand the metabolic pathway: Ethylene glycol is metabolized in the body by the enzyme alcohol dehydrogenase (ADH) into oxoethanoic acid and then further into oxalic acid, which is toxic to the body.
2. Recognize the role of ethanol: Ethanol competes with ethylene glycol for the active site of the enzyme alcohol dehydrogenase (ADH). This competition slows down the metabolism of ethylene glycol into its toxic metabolites.
3. Explain the mechanism: When ethanol is introduced into the bloodstream, it binds preferentially to ADH because it has a higher affinity for the enzyme compared to ethylene glycol. This prevents or reduces the conversion of ethylene glycol into oxoethanoic acid and subsequently into oxalic acid.
4. Describe the outcome: By inhibiting the metabolism of ethylene glycol, the production of toxic oxalic acid is minimized. This allows the body to excrete ethylene glycol more safely through the kidneys before it can be converted into harmful substances.
5. Summarize the treatment rationale: The intravenous administration of ethanol acts as a competitive inhibitor for ADH, effectively protecting the body from the toxic effects of oxalic acid by preventing its formation from ethylene glycol.

Key Concepts

Metabolism of Ethylene Glycol

Ethylene glycol is metabolized in the liver through a series of enzymatic reactions. Initially, it is converted to glycolic acid and then to oxalic acid, which is highly toxic. Understanding this metabolic pathway is crucial for grasping how ethylene glycol ingestion leads to toxicity and the subsequent health risks associated with oxalic acid.

Ethanol as an Antidote

Ethanol is used as an antidote for ethylene glycol poisoning because it competes with ethylene glycol for the same enzyme, alcohol dehydrogenase. By inhibiting this enzyme, ethanol slows down the conversion of ethylene glycol into its toxic metabolites, thereby reducing the formation of oxalic acid and mitigating its harmful effects on the body.

Toxicity of Oxalic Acid

Oxalic acid is a toxic compound that can lead to severe metabolic acidosis and kidney damage when present in high concentrations. It binds to calcium in the body, forming insoluble calcium oxalate crystals, which can precipitate in the kidneys and cause renal failure. Understanding the toxicity of oxalic acid is essential for recognizing the urgency of treating ethylene glycol poisoning.