Bioequivalence and Bioavailability Forum

Hi dshah,

❝ As per standard SOP - "If the response of internal standard in a sample varies by more than 60% for the isotopically labeled internal standard from the mean ISTD response of CC and QC samples of a particular entire run, then repeat the analysis of the sample under reason Significant variations in response of internal standard"

Let’s try that with Shuanghe’s example:

data          <- read.csv("https://bebac.at/downloads/Post21469.csv",
                          sep = ",", dec = ".")
data          <- data[which(data$type == "C" | data$type == "Q"), c(1:2, 4)]
res           <- cbind(data, mean = mean(data$IS.area))
res$deviation <- sprintf("%+.4f%%", 100*(res$IS.area-res$mean)/res$mean)
print(res, row.names = FALSE)

 injection type  IS.area     mean deviation
         1    C 462564.6 490891.8  -5.7706%
         2    C 427928.5 490891.8 -12.8263%
         3    C 436855.6 490891.8 -11.0078%
         4    C 462800.4 490891.8  -5.7225%
         5    C 467778.6 490891.8  -4.7084%
         6    C 481169.4 490891.8  -1.9806%
         7    C 479012.9 490891.8  -2.4199%
         8    C 435110.2 490891.8 -11.3633%
         9    C 464425.2 490891.8  -5.3915%
        10    C 483497.2 490891.8  -1.5064%
        22    Q 470286.3 490891.8  -4.1976%
        29    Q 479924.4 490891.8  -2.2342%
        36    Q 457085.6 490891.8  -6.8867%
        44    Q 479256.7 490891.8  -2.3702%
        51    Q 462271.3 490891.8  -5.8303%
        58    Q 474794.6 490891.8  -3.2792%
        66    Q 480581.6 490891.8  -2.1003%
        73    Q 463233.0 490891.8  -5.6344%
        80    Q 475543.7 490891.8  -3.1266%
        88    Q 476850.6 490891.8  -2.8604%
        95    Q 470929.6 490891.8  -4.0665%
       102    Q 469649.8 490891.8  -4.3272%
       110    Q 483853.7 490891.8  -1.4337%
       117    Q 543378.7 490891.8 +10.6922%
       124    Q 529264.0 490891.8  +7.8168%
       132    Q 647562.5 490891.8 +31.9155%
       139    Q 602118.0 490891.8 +22.6580%
       146    Q 677244.1 490891.8 +37.9620%

With 60% limited deviation of the quoted SOP there would be no reason to repeat the run.

❝ However - there is no guideline which specifies the limit for variation for IS. Thus, it could be 30/40/50/60 - as per CRO's SOP/requirement/Experience.

Correct. Here only your 30% would “work”.
IMHO, this approach is problematic. It depends on many things: The number of CCs and QCs, where they are placed within the run, etc. In Shuanghe’s example we have 22 before troubles started (according to the broken-stick regression at injection 107) and 6 after. Hence, the overall mean of 490892 is misleading (closer to the 466434 in the 1^st limb than to the 580570 in the 2^nd). You would have to be very restrictive to set the maximum deviation.

Little bit less restrictive if we look only at the QCs (acc. to the FDA’s guidance and the ICH draft):

 injection type  IS.area     mean deviation
        22    Q 470286.3 507990.4  -7.4222%
        29    Q 479924.4 507990.4  -5.5249%
        36    Q 457085.6 507990.4 -10.0208%
        44    Q 479256.7 507990.4  -5.6563%
        51    Q 462271.3 507990.4  -9.0000%
        58    Q 474794.6 507990.4  -6.5347%
        66    Q 480581.6 507990.4  -5.3956%
        73    Q 463233.0 507990.4  -8.8107%
        80    Q 475543.7 507990.4  -6.3873%
        88    Q 476850.6 507990.4  -6.1300%
        95    Q 470929.6 507990.4  -7.2956%
       102    Q 469649.8 507990.4  -7.5475%
       110    Q 483853.7 507990.4  -4.7514%
       117    Q 543378.7 507990.4  +6.9663%
       124    Q 529264.0 507990.4  +4.1878%
       132    Q 647562.5 507990.4 +27.4753%
       139    Q 602118.0 507990.4 +18.5294%
       146    Q 677244.1 507990.4 +33.3183%

❝ The interesting thing could be - whether the QC's analyte/IS standard response are within acceptable range - i.e. whether the QC's were acceptable?

In Shuanghe’s example the run passed. AFAIK, the CRO didn’t assess the IS response at all.

❝ I am wondering what other things can be directly correlated …

Some possibilities were discussed before.

❝ … and what can be the reason for CRO's acceptability of variation in IS response?

I can only guess (arbitrary order):

• Not mentioned in any guideline, nothing to worry about.
  
• Followed the SOP blindly. The run passed all criteria, what’s the problem?
  
• Bad science.
  Back in the days were bioanalysts were proud of their scientific attitudes, such a run would definitely have started ringing the alarm bell.

Shuanghe is on vacation. Maybe he can share some insights once back.