Which administration route provides an immediate peak concentration by bypassing absorption phase?

• A. Oral
• B. Subcutaneous
• C. IV bolus
• D. Intramuscular

Answer: (C)

The key idea is that peak concentration depends on how quickly the drug enters the systemic circulation. Delivering a drug directly into the bloodstream bypasses any absorption step, so there is no lag before the drug appears in the plasma. An IV bolus injects the entire dose into the venous system instantly, giving an immediate plasma concentration equal to Dose/Vd at time zero. After this instant, the concentration then declines due to distribution into tissues and eventual elimination.

In contrast, injections given into muscle or under the skin require the drug to be released from the injection site and absorbed into the bloodstream, creating an absorption phase. This slows the rise to peak concentration and produces a delayed Tmax. Oral dosing must also pass through the gastrointestinal tract, undergo absorption, and often first-pass metabolism, further delaying and sometimes reducing the peak.