Which route can bypass first-pass metabolism in drug administration?

The parenteral route of drug administration bypasses first-pass metabolism because it delivers medications directly into the systemic circulation, typically through injections (such as intravenous, intramuscular, or subcutaneous). This method avoids the gastrointestinal tract and the hepatic portal circulation, where drugs are often metabolized by the liver before reaching systemic circulation.

In contrast, oral administration subjects drugs to first-pass metabolism, as they must first pass through the digestive system and liver. Topical administration may also avoid first-pass metabolism, but the absorption may not be consistent across various applications. Rectal administration can partially bypass first-pass metabolism, as some of the drug enters systemic circulation directly, but it does not completely avoid the liver's metabolizing effects.

Thus, the parenteral route is the most effective in ensuring that the maximum amount of active drug reaches the bloodstream without being altered by metabolic processes in the liver before it acts on its target.