Bioequivalence and Bioavailability Forum • Adjusted dilution?

Adjusted dilution? [Bioanalytics]

posted by Helmut – Vienna, Austria, 2012-02-13 14:29 (4856 d 22:45 ago) – Posting: # 8118
Views: 7,076

Dear Auditor!

❝ ❝ How to you do that (“appropriate dilution”)?

❝ in that we are targeting required concentration. After acheiving that concentration we prepare remaining level of the curve by serial dilution. this way we always prepare all the level within the establish calibration curve.

Do you mean something like this?
Validation: 20.1 mg → 100 mL (primary stock 201 µg/mL)
500 µl → 100 mL (spiking stock 1.005 µg/mL)
1 ml plasma + 2/4/8/16/32 µL → 2.010/4.020/8.040/16.08/32.16 ng/mL
Study 1: 19.9 mg → 100 mL (primary stock 199 µg/mL)
505 µl → 100 mL (spiking stock 1.00495 µg/mL);
1 ml plasma + 2/4/8/16/32 µL → 2.010/4.020/8.040/16.08/32.16 ng/mL
Study 2: 20.2 mg → 100 mL (primary stock 202 µg/mL)
497 µl → 100 mL (spiking stock 1.00394 µg/mL);
1 ml plasma + 2/4/8/16/32 µL → 2.008/4.016/8.032/16.06/32.13 ng/mL or
498 µl → 100 mL (spiking stock 1.00596 µg/mL);
1 ml plasma + 2/4/8/16/32 µL → 2.012/4.024/8.048/16.10/32.19 ng/mL

Don’t you see problems with the resolution of pipettes?
In the second study you can either go with 497 µl keeping the calibration within the range at the upper end (32.13<32.16) but failing at the lower end (2.008<2.010) – or with 498 µl overrunning slightly at the upper end (32.19>32.16). I would be more concerned about the former (< validated LLOQ).

❝ I am no talking about CDSCO/ DCGI. I am talking about US FDA. In one of the meeting we have discuss this point and they suggest to have all the level within the establish calibration curve.

Nice.

❝ We do not worry about +1% deviation. as we are adjusting concentration by dilution.

Might not work all the time (see above).

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

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Complete thread:

Extrapolation of Calibration Curve auditor 2012-02-10 06:45
- Exact weight Ohlbe 2012-02-10 12:05
  - Exact weight auditor 2012-02-10 15:54
    - Exact weight: impossible Helmut 2012-02-10 17:33
    - Exact weight Ohlbe 2012-02-10 18:10
      - Exact weight Helmut 2012-02-10 19:15
        
        Exact weight auditor 2012-02-11 06:49
        
        What’s the problem? Helmut 2012-02-11 12:59
        
        What’s the problem? ElMaestro 2012-02-11 20:20
        What’s the problem? auditor 2012-02-13 05:35
        
        Adjusted dilution?Helmut 2012-02-13 13:29
        What’s the problem? Aceto81 2012-02-16 10:50
        
        What’s the problem? auditor 2012-02-16 12:23
        ±5%? Helmut 2012-02-16 13:24
        
        weight pharmino 2012-02-17 21:24
        
        API/formulation Helmut 2012-02-18 13:34