Which substance is metabolized to calcium?

• A. Ethylene glycol
• B. Acetaminophen (Tylenol)
• C. Benzene
• D. Cyanide

Answer: (A)

Ethylene glycol is converted in the liver through a sequence of steps that ultimately yields oxalic acid. Oxalic acid has a strong affinity for calcium and readily binds it to form calcium oxalate. This is why the substance is described as being metabolized to calcium-containing compounds even though the immediate metabolite is oxalate. Calcium oxalate crystals can precipitate in the kidneys, contributing to renal injury and can lower free calcium levels in the body.

Clinically, ethylene glycol poisoning presents with symptoms of CNS depression, metabolic acidosis, and kidney damage, often with detectable calcium oxalate crystals in the urine. Treatment aims to block the formation of oxalate by inhibiting the initial metabolic step (for example, with fomepizole or ethanol) and to manage acidosis and any resulting electrolyte disturbances, including hypocalcemia if it develops.

Other substances listed don’t form calcium oxalate as a key downstream product; their toxic effects arise from different metabolic pathways (for example, acetaminophen through a reactive hepatotoxic metabolite, benzene through bone marrow toxicity, cyanide through inhibition of cellular respiration). The connection here is the downstream formation of a calcium-containing metabolite, specifically calcium oxalate from oxalate derived from ethylene glycol.