Bioequivalence and Bioavailability Forum

Dear Thirupathi!

❝ Is any time limit for withdrawal of ambulatory sample? If yes please mention the reference for the same.

IMHO the only reference stating a maximum deviation is given in the current European Guideline:

In multiple-dose studies, the pre-dose sample should be taken immediately before (within 5 minutes) dosing and the last sample is recommended to be taken within 10 minutes of the nominal time for the dosage interval to ensure an accurate determination of AUC_(0-τ).

However, for most formulations τ will be ≤24 h – so no ambulatory setting here.
The actual method depends on the PK of the drug and the sampling schedule. Generally I would use any possible sample. However, in a truncated AUC setting a delayed sample my lead to a substantial bias of the subject’s T/R-ratio. In such a case I would either limit the allowed time frame, or – probably better – draw the sample and use an estimate (lin/log interpolate) for AUC_t.
See also this post and related ones.