Which of the following is NOT a common route of drug administration?

Subcutaneous administration is indeed a common route for drug delivery, but the question is asking for the option that is NOT commonly recognized as a standard route. The oral, intravenous (IV), and intramuscular (IM) routes are widely used in clinical practice and pharmacology. Oral administration is one of the most frequently used routes due to its convenience and safety. Intravenous administration allows for rapid onset and direct delivery into the bloodstream, which is essential for many treatments. Intramuscular administration is also commonly employed for vaccines and certain medications that require slower absorption.

While subcutaneous administration is utilized for certain drugs (like insulin or some vaccines), it might be less recognized in comparison to the other routes listed, especially in discussions about standard practices. Hence, in the context of this question, subcutaneous administration may be perceived as less common when discussing major routes.