Which route of administration is likely to result in the highest bioavailability?

Intravenous administration is likely to result in the highest bioavailability because it delivers the drug directly into the bloodstream, allowing 100% of the active compound to enter circulation immediately. This bypasses the barriers that other routes of administration face, such as absorption through the gastrointestinal tract or the potential for first-pass metabolism in the liver, which can significantly reduce the amount of drug that ultimately reaches systemic circulation.

In contrast, oral administration must navigate the digestive system and is subject to various factors that can affect absorption, such as pH levels and the presence of food. Similarly, administration via intramuscular or subcutaneous routes involves absorption processes through muscle or subcutaneous tissues, which can vary based on the drug's properties and the injection site. Both these routes typically have bioavailability that is less than that of intravenous administration, primarily due to the absorption delay and potential for incomplete absorption.

Thus, intravenous administration is uniquely positioned to ensure maximum bioavailability and immediate therapeutic effect.