saipraveen7
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India,
2013-07-24 18:45
(4325 d 04:08 ago)

Posting: # 11050
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 selection of appropriate matrix for BA/BE studies [Bioanalytics]

On what basis appropriate matrix (whole blood, plasma, serum, urine, CSF etc.) is selected for method development and sample analysis in BA/BE studies



- P.Sai Praveen
Bio-analytical Chemist
Helmut
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Vienna, Austria,
2013-07-24 20:34
(4325 d 02:19 ago)

@ saipraveen7
Posting: # 11054
Views: 3,847
 

 Mainly plasma

Hi Sai!

❝ On what basis appropriate matrix (whole blood, plasma, serum, urine, CSF etc.) is selected for method development and sample analysis in BA/BE studies


Depends on the PK of the drug and the limitations of the analytical technology.
  • Whole blood: Very rarely used. In some cases the drug bind strongly to erythrocytes and free fraction in plasma is bot low and highly variable. Furthermore, only the ery-fraction is clinically relevant. Example: chlorthalidone.
  • Serum: Rarely used. Only if you face analytical problems with all (!) potential anticoagulants, the drug is stable till complete clotting, and you can exclude back-conversion of metabolite(s). Even if you master all these obstacles likely you will see turbid matrix after thawing, which gets even worse in validating freeze-thaw-cycles. I haven’t seen a method in serum for years.*
  • Plasma: That’s the way to go. Any anticoagulant which passes validation is fine.
  • Urine: History. Haven’t seen a method (in BE of course; PK is another cup of tea) for ages. BE based on urine data is only reasonable if the drug is excreted unchanged (low first pass and/or presystemic metabolization). Was used for bisphosphonates in the past (BA <2%). Since it is very difficult to assess the rate of absorption from urine, EMA accepted extent of absorption from urine (cumulative amount) but still wanted to see Cmax from plasma.
  • CSF: Never. Unethical.
  • Other stuff: There are some studies published with exotic matrices: Saliva, tears, … These studies essentially tried to demonstrate correlation with plasma, allowing noninvasive therapeutic drug monitoring. In BE: Never.


  • Nitsche V, Schütz H, Eichinger A. Rapid high-performance liquid chromatographic determination of nifedipine in plasma with on–line precolumn solid-phase extraction. J Chromatogr, Biomed Appl. 1987;420(1):207–11. doi:10.1016/0378-4347(87)80175-5.
    We used the method (validated for serum) in ten thousands of samples, but occasionally had issues with precipitated protein even in a cooled autosampler. So we switched to plasma. In the cross-validation we discovered that the between-method bias was close to nil, but the variability in plasma was more than twice as high compared to serum. Tried many anticoagulants, always the same story – never found out the reason. At the end we accepted the higher variability and rarely had blocked pre-columns again. ;-)

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jag009
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NJ,
2013-07-25 01:02
(4324 d 21:50 ago)

@ Helmut
Posting: # 11057
Views: 3,818
 

 Mainly plasma

Hi Helmut,

Urine: History. Haven’t seen a method (in BE of course; PK is another cup of tea) for ages. BE based on urine data is only reasonable if the drug is excreted unchanged (low first pass and/or presystemic metabolization). Was used for bisphosphonates in the past (BA <2%). Since it is very difficult to assess the rate of absorption from urine, EMA accepted extent of absorption from urine (cumulative amount) but still wanted to see Cmax from plasma.


KCl?

john
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Vienna, Austria,
2013-07-25 02:05
(4324 d 20:47 ago)

@ jag009
Posting: # 11059
Views: 3,877
 

 Mainly plasma

Hi John,

❝ ❝ Urine: History.


❝ KCl?


Oh no, how could I forget such a goody? Thanks for reminding me.

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