Final answer:
Ethylene glycol poisoning is likely responsible for the observed symptoms due to its metabolism to toxic acid metabolites, particularly glycolic acid and oxalic acid, which can lead to metabolic acidosis and kidney damage.
Step-by-step explanation:
The 56-year-old man's symptoms of lethargy, confusion, vomiting, metabolic acidosis, back pain, gross hematuria, and oliguria, combined with the knowledge from extracted information, suggest a diagnosis of ethylene glycol poisoning. Ethylene glycol is metabolized to glycolic acid, then to glyoxylic acid and finally to oxalic acid, which can bind with calcium and form crystals, causing kidney toxicity and damage. The toxicity of ethylene glycol appears 24 to 72 hours after ingestion and leads to symptoms such as metabolic acidosis due to the accumulation of its acid metabolites, encephalopathy and possibly acute kidney failure within 72 hours if not treated appropriately. Unlike acetaminophen and aspirin, which have different metabolic pathways and toxicities, ethylene glycol toxicity fits the clinical scenario provided.