A patient ingests a large dose of pills and presents with nausea, vomiting, abdominal pain, hypotensive shock, anion gap metabolic acidosis, and hematemesis. What was most likely ingested?

The presentation described in the scenario aligns closely with iron ingestion. When a large dose of iron is ingested, it can result in severe gastrointestinal toxicity, including symptoms such as nausea, vomiting, abdominal pain, and hematemesis. Additionally, iron toxicity can lead to metabolic acidosis and hypotensive shock due to the systemic effects of iron on body tissues.

Iron poisoning typically causes an anion gap metabolic acidosis due to lactic acidosis from tissue hypoxia, as well as the direct effects of iron on cellular metabolism. Early symptoms can resemble those of gastrointestinal irritation, but as the condition progresses, it can lead to more severe complications, including shock due to cardiovascular collapse.

In contrast, aspirin ingestion can cause metabolic acidosis as well, but it usually presents with respiratory alkalosis initially due to hyperventilation. Acetaminophen toxicity presents differently, mainly impacting the liver and leading to hepatic failure over a longer period, while ibuprofen tends to cause less severe immediate symptoms, mainly affecting the renal system or causing gastrointestinal irritation. Therefore, the combination of symptoms and the context of toxicity point clearly towards iron as the most likely agent involved in this case.