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Smitha
Junior

India,
2018-11-29 11:22

Posting: # 19657
Views: 644
 

 Concentration-time graphs and higher last sampling time point [PK / PD]

Hello all,

I have 2 questions on PK for a BE study
  1. Sometimes, the last quantifiable concentration is higher than the preceding concentration in the elimination phase.
    1. What would be the impact of such a profile?
    2. Are there any regulatory requirements on how these need to be handled?
    3. If the guideline or the CRO SOP does not address this issue, is it acceptable to accept the data as is? Does it need to be addressed in an SOP/protocol?
  2. For a BE study, a window period is given for the sampling time points and usually most CROs use the scheduled time point if the sampling deviation is within the window period to plot the concentration-time graphs. The actual sampling time point is used in the graphs only if the sampling is outside the window period.
    1. If the actual time-point is used even if the sampling deviation is within the window period, is it appropriate? Is there an impact on the PK data e.g AUC?
    2. Are there any regulatory requirements on how these need to be handled?

Would appreciate the members opinions on the above points.

Thank you.

Regards,
Smitha
ElMaestro
Hero

Denmark,
2018-11-29 12:15

@ Smitha
Posting: # 19660
Views: 598
 

 Concentration-time graphs and higher last sampling time point

Hello Smitha,

» 1. Sometimes, the last quantifiable concentration is higher than the preceding concentration in the elimination phase.
» a. What would be the impact of such a profile?
» b. Are there any regulatory requirements on how these need to be handled?
» c. If the guideline or the CRO SOP does not address this issue, is it acceptable to accept
» the data as is? Does it need to be addressed in an SOP/protocol?

There is no specific guidance on such matters. It is quite common see what you are observing here. I come across it reasonably often with inhalation and nasal products.
It is always a good idea to have an SOP, but what to put in that SOP is of course tricky. Unless you have a reason to distrust the point (a better reason than PK-expectation alone) then you will need to just work with the value you have. It may cause you to estimate a negative t½, and again, that is just how it is, however unlikely it otherwise that the body starts synthesizing an exogenous molecule.
If you have an SOP stating that in such cases you will do an investigation then you demonstrate ability to reflect and react objectively. Search the forum for aspects like reanalysis as part of the investigation and the difference between recording and reporting in the absence of a cause. It is a mine field and you need to decide whether you want to take guidelines literally or apply some degree of common sense with all the danger that entails :-D


» 2. For a BE study, a window period is given for the sampling time points and usually most CROs use the scheduled time point if the sampling deviation is within the window period to plot the concentration-time graphs. The actual sampling time point is used in the graphs only if the sampling is outside the window period.
»
» a. If the actual time-point is used even if the sampling deviation is within the window
» period, is it appropriate? Is there an impact on the PK data e.g AUC?

I think it is common to use the nominal point for both plotting and AUC-calculation when the sample is inside the window (note: not all CROs apply windows). Otherwise use actual time for both.

» b. Are there any regulatory requirements on how these need to be handled?

No guidance has that level of granularity, as far as I know.

if (3) 4

x=c("Foo", "Bar")
b=data.frame(x)
typeof(b[,1]) ##aha, integer?
b[,1]+1 ##then let me add 1



Best regards,
ElMaestro

"(...) targeted cancer therapies will benefit fewer than 2 percent of the cancer patients they’re aimed at. That reality is often lost on consumers, who are being fed a steady diet of winning anecdotes about miracle cures." New York Times (ed.), June 9, 2018.
Smitha
Junior

India,
2018-11-30 06:43

@ ElMaestro
Posting: # 19663
Views: 543
 

 Concentration-time graphs and higher last sampling time point

Thank you ElMaestro
Helmut
Hero
avatar
Homepage
Vienna, Austria,
2019-02-02 17:30

@ ElMaestro
Posting: # 19849
Views: 134
 

 Concentration-time graphs and NCA

Hi ElMaestro & Smitha,

» » 2. a. If the actual time-point is used even if the sampling deviation is within the window
» »       period, is it appropriate? Is there an impact on the PK data e.g AUC?
»
» I think it is common to use the nominal point for both plotting and AUC-calculation when the sample is inside the window (note: not all CROs apply windows). Otherwise use actual time for both.

I suggest to always use the actual time points (individual plots and NCA) and scheduled ones only for summary (by treatment) plots. Only once I saw a report where medians of actual time points were used. IMHO, a little bit over the top.

A note on “time allowance windows”. In most CROs the actual time point has to be recorded in the CRF anyhow. Only if a deviation from the scheduled time is larger than allowed, an explanation has to be given in the CRF (see also this post).

Cheers,
Helmut Schütz
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