Which route yields the fastest onset of action by bypassing first-pass metabolism?

• A. Intravenous
• B. Intramuscular
• C. Oral
• D. Sublingual

Answer: (A)

The fastest onset with bypassing first-pass metabolism occurs when the drug is delivered directly into the bloodstream. Intravenous administration puts the drug into systemic circulation immediately, so plasma levels rise instantly and the effect is felt almost immediately.

Other routes that bypass the liver on the first pass, such as sublingual and intramuscular, still require absorption into the bloodstream, which introduces a small delay compared to IV. Oral administration undergoes extensive hepatic first-pass metabolism and relies on GI absorption, leading to a slower onset.

So, intravenous administration yields the quickest onset.