ANDA or NDA? [Design Issues]
❝ 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
- you will analyze the data only by NCA,
- you know that the drug follows linear PK, and
- 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.
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