First-pass metabolism occurs with which route?

Subcutaneous administration involves injecting a drug into the fatty tissue just beneath the skin. While this route allows for absorption into the bloodstream, it bypasses the gastrointestinal tract and liver initially, thus avoiding first-pass metabolism. The drug enters systemic circulation more directly, leading to higher bioavailability compared to oral administration.

Intramuscular injections deliver medications directly into muscle tissue, where they are absorbed into the bloodstream. Similar to subcutaneous routes, intramuscular administration does not involve the gastrointestinal tract and liver until after the drug enters systemic circulation, thereby avoiding first-pass metabolism.

Intravenous administration delivers a drug directly into the bloodstream, providing immediate systemic availability. Since there is no passage through the gastrointestinal tract or liver before entering circulation, intravenous routes completely bypass first-pass metabolism, ensuring the full dose of the drug reaches the systemic circulation.