Which factor would shift a concentration-time curve downward (lower plasma levels)?

Which factor would shift a concentration-time curve downward (lower plasma levels)?

• A. Greater absorption
• B. Greater elimination
• C. More drug administered
• D. Oral administration instead of IM

Answer: (B)

A downward shift in the concentration-time curve means lower plasma drug levels at any given time after dosing. This happens when the drug is cleared from the body more quickly. In pharmacokinetics, when elimination is faster, the rate constant for removal increases, making the exponential decline steeper. That means plasma concentrations fall faster, resulting in a lower curve overall (lower Cmax and lower concentrations at later times). Greater absorption would raise plasma levels because more drug enters circulation, so the curve shifts upward. Administering more drug also increases exposure, pushing the curve upward. Switching routes (oral vs intramuscular) can affect how much drug reaches the bloodstream (bioavailability) and thus peak levels, but the direct factor that creates a consistent downward shift is increased elimination, which speeds clearance from the body.

A downward shift in the concentration-time curve means lower plasma drug levels at any given time after dosing. This happens when the drug is cleared from the body more quickly. In pharmacokinetics, when elimination is faster, the rate constant for removal increases, making the exponential decline steeper. That means plasma concentrations fall faster, resulting in a lower curve overall (lower Cmax and lower concentrations at later times).

Greater absorption would raise plasma levels because more drug enters circulation, so the curve shifts upward. Administering more drug also increases exposure, pushing the curve upward. Switching routes (oral vs intramuscular) can affect how much drug reaches the bloodstream (bioavailability) and thus peak levels, but the direct factor that creates a consistent downward shift is increased elimination, which speeds clearance from the body.