Bioequivalence and Bioavailability Forum

Hi John,

❝ If you are being asked to design a PK study to capture single dose and SS PK profiles for a drug product, which dosing and sampling design would you use?

It depends on which question you want to answer.

❝ A) On Day 1 dosing, PK sample from time 0 to X (wait a day to a few days or whatever so to capture 1/2 life). Repeat dosing for x number of days to hit steady state (while collecting predose samples to assess SS), then capture SS pk profile from 0 - x hours as per dosing interval (if dosing interval 6 hours then stop at 12 hrs).

Fine and the standard approach if

1. you will analyze the data only by NCA,
   
2. you know that the drug follows linear PK, and
   
3. there are no circadian variations in PK (otherwise, you have to administer according to the intended dosing regimen in SS and sample for 24 hours).

❝ B) Capture day 1 PK from time 0 to end of dosing interval, repeat dosing for x # of days (base on dosing interval) to hit SS. On last day of dosing capture time 0 - x (x = whatever hrs needed to fully capture the elimination phase + half-life).

To characterize the PK of a new drug by PK modeling you would always go with this approach and sample as long as possible. Funky things may happen in nonlinear PK (auto-induction / -inhibition, capacity-limited elimination, …); see this example.