Which of the following routes does NOT involve the gastrointestinal tract?

The route that does not involve the gastrointestinal tract is the intramuscular route. Intramuscular administration involves delivering medication directly into the muscle tissue, allowing it to be absorbed into the bloodstream. This method bypasses the gastrointestinal system entirely, as the drug is not introduced into the digestive tract at any point.

In contrast, oral and rectal routes do involve the gastrointestinal tract. Oral administration requires the medication to pass through the digestive system for absorption, while rectal administration introduces the drug into the rectum, which is part of the gastrointestinal system. The sublingual route involves placing the medication under the tongue, where it dissolves and is absorbed directly into the bloodstream, bypassing the gastrointestinal tract but still being associated with it in a broader sense.

Thus, the key distinguishing factor is that the intramuscular route directly accesses the systemic circulation through muscle tissue rather than traversing the gastrointestinal tract.