Which route provides 100% bioavailability?

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

Answer: (A)

Bioavailability is the fraction of an administered dose that reaches the systemic circulation in active form. Delivering a drug directly into the bloodstream by intravenous administration bypasses all the absorption barriers—the gastrointestinal tract, intestinal lining, and first-pass metabolism in the liver. Because nothing has to be absorbed first, the entire dose that is intended to reach the circulation does so, giving 100% bioavailability.

Other routes involve some degree of absorption, first-pass effect, or distribution limitations, so their systemic availability is typically less than complete. Sublingual and intramuscular routes bypass the liver to some extent but still rely on absorption into the bloodstream, which introduces variability. Oral administration must cross the GI tract and often undergo significant first-pass metabolism, further reducing bioavailability.