Bioequivalence and Bioavailability Forum

BRN
☆

Turkey,
2014-02-10 14:48
(4089 d 02:45 ago)

Posting: # 12375
Views: 10,007

Pooled Sample Analysis in WinNonlin [Software]

Dear All,

I'm trying to use WinNonlin 6.3 and analyse a data set of pooled samples but getting an error message like that:
There was an error while executing Workflow.Bioequivalence

Core Warning Messages: 0

Core Error Messages: 2

ERROR 11071: Error in Variance Matrix. Model may be over-specified.

ERROR 11071: Error in Variance Matrix. Model may be over-specified.

I used the default settings of average crossover design. Details of sample collection is below. Why I'm getting this error message? Could you please suggest how to proceed with the pooled sample analysis?

Thank you!
BRN

Pooled Sample Collection Design:
After collecting the plasma from each subject who received the same product (T or R), for each time point, plasma samples of all subjects were mixed in a tube and this constituted an average concentration of that time point. Same was done for all time points. At the end I have one concentration for each time point for each product. Same was repeated in the period 2.

While entering the data, I considered one pool as the first subject and the second pool as the second subject and tried to run the analysis with 2 subjects 2 periods.

—
Regards,
BRN

Helmut
★★★

Vienna, Austria,
2014-02-10 15:27
(4089 d 02:06 ago)

@ BRN
Posting: # 12376
Views: 8,025

Forget Pooled Sample Analysis

Post reply

Merhaba BRN,

❝ I used the default settings of average crossover design. Details of sample collection is below.

❝ After collecting the plasma from each subject who received the same product (T or R), for each time point, plasma samples of all subjects were mixed in a tube and this constituted an average concentration of that time point. Same was done for all time points. At the end I have one concentration for each time point for each product. Same was repeated in the period 2.

Are you trying to work according to this paper?

Hundt HKL, Schall R, Luus HG, Müller FO. Considerable cost savings through the analysis of pooled plasma samples in bioequivalence studies that fail to show bioequivalence. Int J Clin Pharm Ther Toxicol. 1993;21(7):331–6. PMID: 8370632

❝ While entering the data, I considered one pool as the first subject and the second pool as the second subject and tried to run the analysis with 2 subjects 2 periods. Why I'm getting this error message?

This can’t work; don’t blame the software. Homework: How many degrees of freedom do you expect?

❝ Could you please suggest how to proceed with the pooled sample analysis?

You could only work according to the paper, i.e. calculate the ratio of the two pooled AUCs and (assuming a maximum CV) following Table 1 in order to decide whether it makes sense to proceed with analyzing subject’s samples or stop the trial. This method was fashionable for a short period of time decades ago, but was quickly abandoned for the following reasons:

You’ll get an unbiased estimate of the AUC-ratio only if there were no drop-outs in the study.
Pooling samples is equivalent to calculating the arithmetic (!) mean of concentrations. It is questionable whether assuming a normal distribution is correct.
No estimate of the C_max-ratio which – due to its generally higher CV – leads the power of the study. Ratio of means ≠ mean of ratios.
The method might lead to stopping a study although it still might have passed – though with lower power than planned. IMHO, not analyzing subject’s samples based on dubious assumptions is not ethical.

Forget it. Doesn’t make sense.

—
Dif-tor heh smusma 🖖🏼 Довге життя Україна!
Helmut Schütz

The quality of responses received is directly proportional to the quality of the question asked. 🚮
Science Quotes

BRN ☆ Turkey, 2014-02-10 15:54 (4089 d 01:39 ago) @ Helmut Posting: # 12377 Views: 7,830	Forget Pooled Sample Analysis Post reply
	Thank you Helmut, I don't have the full paper. I know the client wanted to follow this paper, so I'll buy it and see how it was done decades ago Appreciate your help. BRN — Regards, BRN

Helmut ★★★ Vienna, Austria, 2014-02-10 15:58 (4089 d 01:35 ago) @ BRN Posting: # 12378 Views: 7,849	Forget Pooled Sample Analysis Post reply
	Merhaba BRN, ❝ I know the client wanted to follow this paper, so I'll buy it and see how it was done decades ago If you want I can send you a scan. — Dif-tor heh smusma 🖖🏼 Довге життя Україна! Helmut Schütz The quality of responses received is directly proportional to the quality of the question asked. 🚮 Science Quotes

BRN ☆ Turkey, 2014-02-10 16:11 (4089 d 01:22 ago) @ Helmut Posting: # 12379 Views: 7,829	Forget Pooled Sample Analysis Post reply
	That would be great. I've already sent you my e-mail via PM. Thanks a lot! BRN I didn’t receive a PM. I’ve sent it to your yahoo-account. [Helmut] — Regards, BRN

jag009 ★★★ NJ, 2014-02-10 17:23 (4089 d 00:10 ago) @ Helmut Posting: # 12380 Views: 7,842	Me too! Post reply
	Hi Helmut, Can I get a copy too?

Helmut
★★★

Vienna, Austria,
2014-02-10 17:58
(4088 d 23:34 ago)

@ jag009
Posting: # 12381
Views: 7,895

Crap…

Post reply

Hi John,

❝ Can I get a copy too? :-)

Check your inbox. But it is real crap – not worth the additional analytical efforts. :no:

If you still want to dive in I would suggest to try it with a reasonable number of your past studies. Calculate the means of individual concentrations / treatment and their AUCs, the ratio, and check according to the table (based on the CV you used in planning the study) whether you would have stopped the study or not. Good luck – and tell us how many false positives you observed…

PS: In the last century when we applied this procedure a couple of times (Sponsor’s wish – “Considerable cost savings” in the title!) we faced some obstacles. When taking aliquots the accuracy of the pipetting is not important – as long as it is done precisely. We decided not to leave this on the shoulders of the clinical staff, but delegated an analyst. But: That’s work unblinded for treatment. We had to set up an SOP guaranteeing that this analyst would not analyze the biosamples later on. I’m not sure whether inspectors would believe (!) that she didn’t memorize the randomization scheme and tell it to her colleagues… Trouble on the way.
PPS: What’s the percentage of your studies without a single drop-out?

—
Dif-tor heh smusma 🖖🏼 Довге життя Україна!
Helmut Schütz

The quality of responses received is directly proportional to the quality of the question asked. 🚮
Science Quotes

Ohlbe ★★★ France, 2014-02-10 19:48 (4088 d 21:45 ago) @ Helmut Posting: # 12388 Views: 7,805	Crap… Post reply
	Dear all, ❝ [...] it is real crap – not worth the additional analytical efforts. I heard that the authors of the paper themselves stopped using this procedure quite fast... — Regards Ohlbe

jag009 ★★★ NJ, 2014-02-10 21:27 (4088 d 20:05 ago) @ Helmut Posting: # 12391 Views: 7,824	Crap^2 Post reply
	Totally agreed. More or less it will be a bioanalytical nightmare since the pooled concentration will be high → calibration curve hahaha! One more thing, even the author wrote about the shortcoming of this method, tada! Cmax! Not trying to bad mouth people but how could such article be worth publishing? Again I apologize if I have offended anyone. John

Helmut
★★★

Vienna, Austria,
2014-02-11 14:45
(4088 d 02:48 ago)

@ jag009
Posting: # 12397
Views: 7,740

Crap²

Post reply

Hi John,

❝ More or less it will be a bioanalytical nightmare since the pooled concentration will be high → calibration curve hahaha!

Nope – if you mix small aliquots and analyze the usual volume the concentration will be arithmetic mean of the aliquots.

❝ One more thing, even the author wrote about the shortcoming of this method, tada! Cmax!

Yep. In the few studies where we applied the method it was not stated as a strict requirement in the protocol to stop the study. We had just one case where the method would suggest stopping based on the AUCP-ratio. The sponsor decided to proceed analyzing the subjects’ samples (“We have the budget allocated. Let’s give it a try at least.”) and the study passed…

❝ Not trying to bad mouth people but how could such article be worth publishing?

Let’s not start a discussion about the peer-review process of some (most?) journals. :-D

—
Dif-tor heh smusma 🖖🏼 Довге життя Україна!
Helmut Schütz

The quality of responses received is directly proportional to the quality of the question asked. 🚮
Science Quotes

ElMaestro ★★★ Denmark, 2014-02-11 15:41 (4088 d 01:51 ago) @ Helmut Posting: # 12398 Views: 7,705	Crap² Post reply
	Aaaaah, ❝ ❝ Not trying to bad mouth people but how could such article be worth publishing? ❝ ❝ Let’s not start a discussion about the peer-review process of some (most?) journals. Do I sense a good vitriolic Hötzi-rant coming up?? Sweet! This is going to be great, I'll make some popcorn. When does the show start? — Pass or fail! ElMaestro

jag009 ★★★ NJ, 2014-02-11 18:27 (4087 d 23:06 ago) @ ElMaestro Posting: # 12402 Views: 7,663	Crap² Post reply
	❝ Do I sense a good vitriolic Hötzi-rant coming up?? Sweet! This is going to be great, I'll make some popcorn. When does the show start? I will bring Absinthe.

Helmut
★★★

Vienna, Austria,
2014-02-12 01:57
(4087 d 15:35 ago)

@ jag009
Posting: # 12408
Views: 7,775

OT

Post reply

Folks!

❝ ❝ […] This is going to be great, I'll make some popcorn.

❝ I will bring Absinthe. :party:

Strange color your absinthe has!

❝ ❝ When does the show start?

The main question is not when, but where? If I try to find a place minimizing the distance to our homes I end up in the middle of the Atlantic… Have you ever been to the Azores? No direct flights – shall we opt for hiring bizjets? Will one of our clients reimburse the travel expenses?

I came across this disturbing signboard in Prague, October 2009:

—
Dif-tor heh smusma 🖖🏼 Довге життя Україна!
Helmut Schütz

The quality of responses received is directly proportional to the quality of the question asked. 🚮
Science Quotes

ElMaestro
★★★

Denmark,
2014-02-12 15:03
(4087 d 02:29 ago)

@ Helmut
Posting: # 12409
Views: 7,644

OT

Post reply

Hi Hötzi,

❝ Have you ever been to the Azores? No direct flights – shall we opt for hiring bizjets? Will one of our clients reimburse the travel expenses?

Been there, I can certainly recommend it. Never seen such green grass, I almost wished I was a cow. Perhaps we can ask Informa or IQPC to do the next BA/BE confy out there? Never got it, why it has to be in Budapest every year?!? Good habits die hard, perhaps. Must brainwash James W. a little next time I talk to him. :-D

—
Pass or fail!
ElMaestro

Pooled Sample Analysis in WinNonlin [Software]

Forget Pooled Sample Analysis

Forget Pooled Sample Analysis

Forget Pooled Sample Analysis

Forget Pooled Sample Analysis

Me too!

Crap…

Crap…

Crap^2

Crap²

Crap²

Crap²

OT

OT