Which of the following routes is NOT a common method for administering drugs to patients?

Transcutaneous administration refers specifically to delivering medications through the skin surface, often using patches that release the drug into the bloodstream. Although this method can be used in certain contexts, such as with specific medications like nicotine or hormone patches, it is not as commonly referenced in the context of general drug administration compared to other methods.

In contrast, topical administration involves applying drugs directly to the skin or mucous membranes for localized effect, inhalation allows medications to be delivered through the respiratory tract for systemic or localized lung effects, and intramuscular administration provides a route for delivering drugs into the muscle, often for faster absorption into the bloodstream. These methods are widely practiced in both human and veterinary medicine, which is why transcutaneous is seen as the less common option among these choices.