Which concentration-time profile describes an IV bolus administration?

Which concentration-time profile describes an IV bolus administration?

• A. IV bolus starts high and gradually declines
• B. Constant IV infusion starts at zero and increases to a plateau
• C. IV bolus starts at mid-level and then rises
• D. Constant IV infusion remains constant over time

Answer: (A)

When a drug is given as an IV bolus, it is injected directly into the bloodstream, so the plasma concentration jumps to its highest value at the moment of administration (C0) and then declines as the drug distributes to tissues and is eliminated. This creates a concentration-time plot that starts high right after dosing and gradually falls over time, often with a rapid distribution phase followed by a slower elimination phase. That immediate high concentration followed by a decline best matches the bolus pattern. The other scenarios describe infusion dosing. A constant IV infusion begins at zero and concentration rises toward a plateau as the drug accumulates until input balances elimination. A profile starting at a mid-level and rising implies a delayed input or absorption step, which isn’t present with an IV bolus. A constant infusion that remains perfectly flat would imply steady-state has already been reached, which is not the immediate bolus profile.

When a drug is given as an IV bolus, it is injected directly into the bloodstream, so the plasma concentration jumps to its highest value at the moment of administration (C0) and then declines as the drug distributes to tissues and is eliminated. This creates a concentration-time plot that starts high right after dosing and gradually falls over time, often with a rapid distribution phase followed by a slower elimination phase. That immediate high concentration followed by a decline best matches the bolus pattern.

The other scenarios describe infusion dosing. A constant IV infusion begins at zero and concentration rises toward a plateau as the drug accumulates until input balances elimination. A profile starting at a mid-level and rising implies a delayed input or absorption step, which isn’t present with an IV bolus. A constant infusion that remains perfectly flat would imply steady-state has already been reached, which is not the immediate bolus profile.