PHARM/PCS V5 · Procedure 32
Pharmacokinetics VII: Multiple Dosing from Absorptive Site
For repeated oral doses, find the steady-state mean and peak concentrations and the time to reach 95% of steady state.
What it computes
Computes steady-state mean and peak concentrations for repeated oral (absorptive) dosing. Two modes: approximate (Ka unknown: uses clearance or Vd and half-life) and exact (Ka known: full two-compartment model with peak-time calculation).
Inputs and outputs
You provide
- Dose D and dosing interval T
- Ke, or the half-life
- Fraction absorbed F (default 1)
- Either Vd or clearance
- Ka, if known, for the exact calculation
PHARM/PCS reports
- Steady-state mean and peak concentrations
- With Ka: the time of the peak
- Half-life and the time to reach 95% of steady state
- A concentration-time curve showing accumulation to steady state
When to use it
For a repeatedly dosed oral drug when you need steady-state average and peak levels, the absorptive-route counterpart to multiple IV dosing (Procedure 27). Use the exact mode when a reliable Ka is available (for example, from Procedure 29), the approximate mode when it isn't.
Reading the results
The approximate mode gives the steady-state average well but can't pin the peak timing, which depends on absorption rate; if the peak matters clinically, invest in a good Ka and use the exact mode. As always, steady state assumes roughly 4-5 half-lives of consistent dosing.
Exact or approximate
Leave Ka blank and the procedure uses the approximate formula based on clearance. Supply it and the full two-compartment model runs instead. Either way, the time to 95% of steady state is computed exactly rather than by the rough rule of 4.3 half-lives.
This page describes the procedure. Calculations run inside the licensed PHARM/PCS V5 application. PHARM/PCS is a trademark of MCS Scientific LLC.