Which sequence correctly describes the path of an orally administered drug from ingestion to excretion?

• A. Ingested -> stomach -> intestines -> liver portal circulation -> systemic circulation -> excretion
• B. Ingested -> stomach -> intestines -> liver portal circulation -> some escapes to target, rest excreted
• C. Ingested -> esophagus -> stomach -> pancreas -> liver -> excretion
• D. Ingested -> stomach -> liver -> lungs -> excretion

Answer: (B)

Oral drugs undergo first-pass metabolism in the liver, which shapes how much of the dose actually reaches systemic circulation to reach the site of action. After ingestion, absorption occurs through the GI tract (stomach and intestines) and the drug travels via the hepatic portal circulation to the liver. There, a portion is metabolized before it can reach the rest of the body. The fraction that escapes this first-pass metabolism enters systemic circulation and can reach the target tissues; the remainder is processed and eventually excreted. This is why the sequence that includes absorption through the GI tract, delivery to the liver via portal circulation, and only a portion advancing to systemic circulation (with the rest being excreted) best reflects the real path of an orally administered drug.

The other options misplace absorption or routes of elimination: the esophagus and pancreas aren’t sites of absorption that route drugs to the liver; relying on the lungs for excretion is only accurate for certain volatile substances, not the typical oral drug; and assuming all drug goes directly from liver to systemic circulation ignores first-pass metabolism and its impact on bioavailability.