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Back to the forum  Query: 2018-04-25 00:57 UTC (UTC+2h)
 
nobody
Senior

2018-04-03 09:16

Posting: # 18634
Views: 1,273
 

 Counterintuitive? [Design Issues]

Hy!

Found this Easter egg:

https://link.springer.com/article/10.1007/s11095-018-2387-4?

...only read the abstract, but the findings and Conclusion are not really intuitive to me (still in mild post-prandial coma, I must admit). Why should the most appropriate AUC metric depend on the release rate of the Test product relative to reference?

Any ideas how to wrap my head around this?

Kindest regards, nobody
bebac_fan
Junior

US,
2018-04-03 16:20

@ nobody
Posting: # 18635
Views: 1,116
 

 Counterintuitive?

Hi Nobody,


» Why should the most appropriate AUC metric depend on the release rate of the Test product relative to reference? Any ideas how to wrap my head around this?

I'll take a shot. I am a clinical pharmacologist, so forgive me if I am not speaking the language. I am happy to clarify.

This is regarding a liposomal formulation that has funky kinetics.

A mix of liposomal-bound and free doxorubicin is infused, then some liposomal-bound slowly leaches out (they call this rate REL). Different liposomal formulations can introduce considerable variance in RES, it is reasonable to check out how to detect bad liposomal formulations using unbound + total PK doxorubicin PK samples.

Looking at the model, REL is much smaller than clearance. This is "flip flop kinetics," where the rate and extent of absorption aren't adequately covered by Cmax and AUC. SQ Biologics usually have this - insulins, MABs, etc. In flip flop kinetics, Cmax usually corresponds to the clearance of the drug, and terminal t 1/2 corresponds to the absorption rate - quite opposite to what we're used to.

So given the funky kinetics, the authors simulated a "what if" scenario by changing the RES and saw what NCA parameters were best at identifying it.

If the liposomal formulations leached more quickly (E.g. RELt > RELr), the drug would switch from flip-flop kinetics to standard kinetics.

Attached is an image showing how PK changes SHAPE greatly when changing REL.

[image]

Hope this helps -
BF
nobody
Senior

2018-04-03 21:25

@ bebac_fan
Posting: # 18636
Views: 1,096
 

 Counterintuitive?

Hi BF!

» If the liposomal formulations leached more quickly (E.g. RELt > RELr), the drug would switch from flip-flop kinetics to standard kinetics.

Might be, but not necessarily. Or? ;-)

Why should the ratio of REL influence the appropriate metric for BE? Switching T and R should not influence the test in my opinion...

Kindest regards, nobody
bebac_fan
Junior

US,
2018-04-03 22:43

@ nobody
Posting: # 18637
Views: 1,077
 

 Counterintuitive?

Hi Nobody,

» Why should the ratio of REL influence the appropriate metric for BE? Switching T and R should not influence the test in my opinion...

The BE studies I have seen (I am quite junior), the drugs follow dose-linearity. One convenient result is that the SHAPE of the PK curve generally stays the same under test conditions. That means the tests aren't required to be sensitive for changes in shape.

This drug doesn't follow that assumption for reasons previously discussed. The PK shape changes under small formulation changes (e.g. REL). There is definitely a need for non traditional parameters, as it is conceivable that AUCinf and Cmax may pass, but with wildly (and clinically relevant) differences in shape.

I agree that the test applied should be invariant to T/R or R/T. Perhaps run a test on Tmax - which based on the above image, appears to be sensitive to changes in REL. Or require passing all the tests together.

Cheers,
BF
nobody
Senior

2018-04-04 09:03

@ bebac_fan
Posting: # 18638
Views: 1,005
 

 Counterintuitive?

Hi again!

» I agree that the test applied should be invariant to T/R or R/T.

That's the point. Are these sims utter nonsense or did I miss somethink ;-)

Kindest regards, nobody
Helmut
Hero
Homepage
Vienna, Austria,
2018-04-04 14:49

@ bebac_fan
Posting: # 18641
Views: 962
 

 What is clinically relevant?

Hi BF,

» A mix of liposomal-bound and free doxorubicin is infused, …

Are you sure? I know only liposome-encapsulated formulations (i.e., containing no free doxorubicin).

I agree that the FDA’s guidance (asking for AUC and Cmax of free and liposome-encapsulated doxorubicin) might not sufficiently enough characterize the profiles.

There is no product-specific guidance in Europe so far. However, current regulatory practice on this side of the pond is much more strict.
PK metrics for encapsulated, free, and total doxorubicin:
  • primary: AUC0–t, AUC0–∞, Cmax.
  • secondary: pAUC0–48, pAUC48–t. I have seen discussion with agencies when you fail on the partial AUCs.
PK metrics for the primary metabolite doxorubicinol: As above but supportive only.

Problems are manifold:
  • Blood samples have to be immediately put on ice and stabilized in order to prevent rupture of liposomes during centrifugation. I have seen funky “profiles” of free doxorubicin where some concentrations clearly were an artifact (the corresponding profiles of doxorubicinol were nice).
  • Practically only doxorubicinol is responsible for the effect.
IMHO, encapsulated, free, and total doxorubicin are not relevant from a clinical perspective – only nice to know. I would prefer to assess just the metabolite but all of its PK metrics in a confirmatory manner.

BTW, at the 3rd GBHI conference (Amsterdam, April 12–13) Session IV will be devoted to liposomal parenteral preparations. Let’s wait for regulators’ unfathomable wisdom.

[image]Regards,
Helmut Schütz 
[image]

The quality of responses received is directly proportional to the quality of the question asked. ☼
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nobody
Senior

2018-04-05 08:04

@ Helmut
Posting: # 18643
Views: 871
 

 What is clinically relevant?

Hi Felix Austria!

Yeah, it's complicated, no question. PEG-ylated, non-PEG-ylated on top. Maybe this i.v. modified release formulations are as complicated as inhalative stuff...

But what I was asking for is the finding of the paper that depending on the T/R of the release rate the most appropriate/sensitive parameter should vary. Is that real or not? I can't make sense out of this (without reading the original paper, no 41.59 € worth for me...).

Let's say: if T releases faster than R, take AUCpart 0-24h. But if I switch T and R the same does not apply. Why that? I don't get it....

Kindest regards, nobody
bebac_fan
Junior

US,
2018-04-05 12:19

@ Helmut
Posting: # 18644
Views: 852
 

 What is clinically relevant?

Dear Helmut,

» Are you sure? I know only liposome-encapsulated formulations (i.e., containing no free doxorubicin).

Sure - but in practice, "trauma" from the peristaltic IV pump and the narrow gauge needle can release drug. Further, the biphasic PK profile of unbound dox following liposomal infusion is supportive of an effective 5% IV bolus and 95% liposomal input.

However, it is very cool to hear that this may be an artifact!

» IMHO, encapsulated, free, and total doxorubicin are not relevant from a clinical perspective – only nice to know.

I agree. I believe the free is only clinically relevant. Imposing tests on the bound form is like measuring the amount of drug in the gut (i.e. the "liposome") and in the blood (i.e. unbound in blood).

I am not sure what I would do if I found that total had a much different PK profile, but resulted in same free fractions. Probably explode.

May I add, that I have not found any other forum even tangentially related to clinical pharmacology, pharmacometrics, or drug development that is anywhere as active.
Thanks for the great discussion.

Cheers,
BF
nobody
Senior

2018-04-06 07:22

@ bebac_fan
Posting: # 18646
Views: 766
 

 What is clinically relevant?

....fresh:

https://www.fda.gov/downloads/drugs/guidances/ucm070570.pdf

Although not very detailed on BE, gives an impression that liposomes are no simple formulations re. biopharmaceutics...

Kindest regards, nobody
Helmut
Hero
Homepage
Vienna, Austria,
2018-04-06 14:10

@ bebac_fan
Posting: # 18647
Views: 708
 

 What is clinically relevant?

Hi BF,

» […] in practice, "trauma" from the peristaltic IV pump and the narrow gauge needle can release drug.

Hhm, never thought about that! Though I didn’t see an early “release” in one of my studies: Example Caelyx (50 mg/m2: 72.2 – 109.4 mg), length of infusion 01:17 – 01:53 hours, LLOQ 18 µg/mL (encapsulated doxorubicin: left), 9 ng/mL (free: right).

[image]  [image]

» However, it is very cool to hear that this may be an artifact!

Cool, maybe. Nasty if you want to assess the PK. Below one subject where obviously sumfink went wrong in sample handling at the clinical site (analytical result confirmed from the backup sample).

[image]

[image]

What the heck? The concentration of free doxorubin at 25.5 h is ~25 (!) times the two adjacent concentrations. Since the metabolite is formed from the parent in plasma, it’s clear that we face an artifact.

» » IMHO, encapsulated, free, and total doxorubicin are not relevant from a clinical perspective – only nice to know.
»
» I agree. I believe the free is only clinically relevant.

From a clinical perspective, yes. Given the crazy results I faced in some cases, the metabolite would be more robust – though we would have to sample substantially longer in order to get a reliable estimate of the AUC.

» Imposing tests on the bound form is like measuring the amount of drug in the gut (i.e. the "liposome") and in the blood (i.e. unbound in blood).

Yep.

» I am not sure what I would do if I found that total had a much different PK profile, but resulted in same free fractions. Probably explode.

:-D

» […] I have not found any other forum even tangentially related to clinical pharmacology, pharmacometrics, or drug development that is anywhere as active.
» Thanks for the great discussion.

Thanks from my side as well!

[image]Regards,
Helmut Schütz 
[image]

The quality of responses received is directly proportional to the quality of the question asked. ☼
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bebac_fan
Junior

US,
2018-04-06 18:53

@ Helmut
Posting: # 18648
Views: 686
 

 What is clinically relevant?

Dear Helmut:

I believe the spaghetti plots you posted are actually indicative of a infusion of unbound drug.

Release of the encapsulated form follows first order kinetics and is Sequential - kind of like metabolic clearance from parent --> metabolite.

Luckily, you also posted the parent/metabolite curve for doxorubinol. Because of similarity in process, if no free drug is infused, bound and unbound PK should follow the same general shape we see in parent + metabolite.

The fact that total + free dox concentrations are colinear is pretty strong evidence for co-infusion of bound + unbound. Further, the fact that there isn't a lag time in unbound, as well as a nonlinear shape, is evidence, too.

Thanks,
BF
Helmut
Hero
Homepage
Vienna, Austria,
2018-04-06 20:05

@ bebac_fan
Posting: # 18649
Views: 677
 

 What is clinically relevant?

Hi BF,

» I believe the spaghetti plots you posted are actually indicative of a infusion of unbound drug.
»
» Release of the encapsulated form follows first order kinetics and is Sequential - kind of like metabolic clearance from parent --> metabolite.

Did you notice the different concentrations scales (encapsulated doxorubicin: µg/mL, free: ng/mL)? On the average free is less than 1% of encapsulated. With just three sampling times during infusion I would say it is not possible to separate zero order (encapsulated) from first order (release from the liposomes).

» Luckily, you also posted the parent/metabolite curve for doxorubinol. Because of similarity in process, if no free drug is infused, bound and unbound PK should follow the same general shape we see in parent + metabolite.

What do you mean by bound + unbound? Encapsulated and free?

» The fact that total + free dox concentrations are colinear is pretty strong evidence for co-infusion of bound + unbound.

I still don’t think so. The release can be quite quick. Hence, the shapes looks similar but the concentrations of free doxo are always pretty low compared to encapsulated doxo.

» Further, the fact that there isn't a lag time in unbound, as well as a nonlinear shape, is evidence, too.

Again, I would contradict that. I don’t expect a lag-time. I would rather say that doxo follows Le Chatelier’s principle and is simply driven out from the liposomes due to the concentration gradient (Cliposomes > Cblood).

[image]Regards,
Helmut Schütz 
[image]

The quality of responses received is directly proportional to the quality of the question asked. ☼
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mittyri
Senior

Russia,
2018-04-06 21:36

@ Helmut
Posting: # 18650
Views: 670
 

 Korsmeyer–Peppas’ model

Hi Helmut,

just want to add regarding

» I don’t expect a lag-time. I would rather say that doxo follows Le Chatelier’s principle and is simply driven out from the liposomes due to the concentration gradient (Cliposomes > Cblood).

with a recent paper [1]
Looks like it follows Korsmeyer–Peppas’ model
Release = (CumReleased)/(FinallyReleased) = k*tn

[image]

I know that's endless in vitro attempt but it confirms your suggestion.

To obtain an indirect estimate of plasma concentrations of free doxorubicin after administration of Liposomal Doxorubicin, the reported ratio between doxorubicinol, the major doxorubicin metabolite, and doxorubicin concentration in plasma after administration of standard doxorubicin can be used.
Based on the measurement of doxorubicinol, which usually represents 40–50% of the free doxorubicin concentrations, plasma concentrations of free doxorubicin after liposomal administration remain very low, approximately 0.25–1.25% of the total measured drug. [2]
  1. Fateme Haghiralsadat et al. (2017) A comprehensive mathematical model of drug release kinetics from nano-liposomes, derived from optimization studies of cationic PEGylated liposomal doxorubicin formulations for drug-gene delivery, Artificial Cells, Nanomedicine, and Biotechnology, 46:1, 169–177, doi:10.1080/21691401.2017.1304403.
  2. Gabizon, A., Shmeeda, H. & Barenholz, Y. Clin Pharmacokinet (2003) 42: 419–436. doi:10.2165/00003088-200342050-00002.

Kind regards,
Mittyri
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