How does an intravenous infusion alter the concentration-time profile compared with a bolus dose?

How does an intravenous infusion alter the concentration-time profile compared with a bolus dose?

• A. Gradual rise to a plateau (steady-state) with lower Cmax and no sharp initial peak.
• B. Immediate sharp peak with a higher Cmax.
• C. A slower rise to a plateau with higher exposure.
• D. A plateau is never reached with infusion.

Answer: (A)

When a drug is given by a constant-rate intravenous infusion, it enters the bloodstream continuously rather than all at once. This creates a gradual buildup in plasma concentration as the drug accumulates until the rate of input equals the rate of elimination. The concentration rises exponentially and approaches a plateau called the steady-state concentration (Css), where Css = (input rate) / clearance. Because nothing is injected instantaneously, there is no sharp initial spike in concentration—the peak is reached slowly as the infusion continues, and the maximum during sustained infusion is typically lower than the peak you’d see after a bolus. In contrast, a bolus delivers the entire dose at once, producing an immediate, high Cmax that then declines exponentially as the drug is cleared. The infusion thus yields a smoother, gradual rise to a plateau and avoids the abrupt peak seen with a bolus. So the best description is a gradual rise to a steady-state plateau with no sharp initial peak and a lower Cmax compared with a bolus.

When a drug is given by a constant-rate intravenous infusion, it enters the bloodstream continuously rather than all at once. This creates a gradual buildup in plasma concentration as the drug accumulates until the rate of input equals the rate of elimination. The concentration rises exponentially and approaches a plateau called the steady-state concentration (Css), where Css = (input rate) / clearance. Because nothing is injected instantaneously, there is no sharp initial spike in concentration—the peak is reached slowly as the infusion continues, and the maximum during sustained infusion is typically lower than the peak you’d see after a bolus.

In contrast, a bolus delivers the entire dose at once, producing an immediate, high Cmax that then declines exponentially as the drug is cleared. The infusion thus yields a smoother, gradual rise to a plateau and avoids the abrupt peak seen with a bolus.

So the best description is a gradual rise to a steady-state plateau with no sharp initial peak and a lower Cmax compared with a bolus.