Final answer:
Thiopental is the medication that primarily terminates its action by redistribution. It quickly redistributes from the brain to other tissues after inducing anesthesia, leading to a decrease in its effects.
Step-by-step explanation:
The question relates to which medications primarily terminate their action by redistribution. Redistribution is when the drug moves away from its site of action to other tissues, diminishing its effect without the need for the drug to be completely metabolized or excreted. Among the options given, thiopental is a barbiturate that is known to have a high lipid solubility and acts rapidly to induce anesthesia. After its initial distribution, thiopental's anesthetic effect decreases quickly due to redistribution from the brain to other tissues such as muscle and fat.
Option 1, propofol, and Option 4, ketamine, are also intravenous anesthetics, but they do not primarily terminate their action through redistribution. Option 3, remifentanil, is an opioid that is rapidly metabolized by blood and tissue esterases and, thus, does not rely primarily on redistribution for the termination of its effects.