Bioequivalence and Bioavailability Forum

Hi Ken,

❝ In a BE study involving 26 subjects […] the last 6 subjects had many points above ULOQ.

Sometimes concentrations in a few subjects are higher than anticipated, but this should occur at random. Why in the last six subjects? What makes them so special? If I would be an inspector that would ring my alarm bell. I would ask R how likely the observed pattern could occur by pure chance (the code takes a good while to complete; be patient – 28 minutes on my machine):

set.seed(123456)
n   <- 1e8                      # no. of simulations; at least 1 mio needed
x   <- c(rep(0, 20), rep(1, 6)) # 20 "normal" subjects and 6 ">ULOQ"
obs <- 0                        # counter for the "last 6" pattern
for(j in 1:n) { if(sum(tail(sample(x), 6)) == 6) obs <- obs + 1 }
cat("p =", signif(obs/n, 4), "\n")

IMHO p = 4.49·10^–6 should trigger an internal investigation. Some ideas/questions:

• Was the clinical part of the study performed in groups? If yes, which was the size of groups?
  
• Any documented events in the analytical batches (cali­bra­tion, IS addition, detector response, etc.)?
  
• Look at the subjects’ pre-/post-study lab exams. High lipid parameters in these subjects (matrix effects in LC/MS-MS if no stable isotope IS was used)?
  
• Were the last six subjects underweight females and the others Sumo-wrestlers?