PHARM/PCS V5 · Procedure 27
Pharmacokinetics II: Multiple Intravenous Injections
For repeated IV doses at a fixed interval, find the steady-state peak, trough, and mean concentrations, and how many doses it takes to get there.
What it computes
For a drug eliminated exponentially, given in repeated IV doses of amount I at equal time intervals t′, computes the steady-state peak (Cu), trough (Cl), and mean (C̄) plasma concentrations, and the number of doses to reach a specified fraction of Cu.
Inputs and outputs
You provide
- Dose I and volume of distribution V
- Elimination rate constant ke
- Dosing interval t′
- The target percentage of the steady-state peak
PHARM/PCS reports
- Steady-state peak Cu, trough Cl, and mean concentration
- The fraction remaining at the end of each interval
- The number of doses needed to reach your target percentage of the peak
- A concentration-time curve across doses, with peak and mean levels marked
When to use it
For intermittent IV bolus dosing when you need the steady-state peak, trough, and average, the basis for choosing a dose and interval that stay inside a therapeutic window. Compare with continuous infusion (Procedure 26) and with absorptive-site multiple dosing (Procedure 32).
Reading the results
The peak-to-trough swing is driven by the interval relative to half-life: dose more frequently (relative to t½) to flatten the swing, less to widen it. The doses-to-reach-a-fraction-of-Cu answer again reflects the 4-5 half-life rule for accumulation.
A regimen you can see
Change the dose or the interval and the plotted peaks and troughs move with it. That makes the procedure a quick classroom demonstration of why dosing more often relative to the half-life flattens the swing, and why accumulation takes several half-lives. Results match the 1986 program to every printed digit.
This page describes the procedure. Calculations run inside the licensed PHARM/PCS V5 application. PHARM/PCS is a trademark of MCS Scientific LLC.