PharmPK Discussion - Sample size for BE studies

• On 17 Sep 2007 at 14:49:39, "Mathew Francis" (mathewspf007.-at-.gmail.com) sent the message
  

  
  Dear all,
  
  I am new to this clinical field. Any one help me to clear some doubts
  in sample size calculation for a 2 x 2 crossover design.
  
    I know only the Cmax value of the drug from the literature. It is
  around 42.34plus or minus 13.27.
  
  How I can calculate the intra subject CV from this Cmax value? (is it
  required for Sample Size calculation?)
  
  which value of "delta" we commonly used for calculating Sample Size?
  
  there are different sample size formulas for addictive model and
  multiplicative model? which model we commonly used? why?
  
  Mathews
  
  

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• On 18 Sep 2007 at 09:48:40, Navdeep Coelho (Navdeep.Coelho.-at-.biovail.com) sent the message
  

  
  Dear Mathew,
  
  You need an estimate of the intra-subject CV from ANOVA for
  calculating the sample size. However, you can get a ball park
  estimate of the intra-subject CV by taking 60% of the inter-subject
  variability (sd/mean). I personally do not use this method because
  its not robust.
  Please see the paper by Steven A Julious, "Tutorial in Biostatistics
  - Sample sizes for clinical trials with normal data." Its an
  excellent reference.
  
  Nav Coelho
  Biovail Contract Research
  
  

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• On 18 Sep 2007 at 19:45:07, Helmut Schuetz (helmut.schuetz.-a-.bebac.at) sent the message
  

  
  The following message was posted to: PharmPK
  
  Dear Navdeep & Mathews
   > ... However, you can get a ball park
   > estimate of the intra-subject CV by taking 60% of the inter-subject
   > variability (sd/mean). I personally do not use this method because
   > its not robust.
  
  I don't think this '60%-rule by-thumb' is of any good. ;-)
  See this two posts:
  
  http://forum.bebac.at/forum_entry.php?id=921
  http://forum.bebac.at/forum_entry.php?id=925
  
  Best regards,
  Helmut
  
  --
  Ing. Helmut SchA\0x00tz
  BEBAC - Consultancy Services for
  Bioequivalence and Bioavailability Studies
  Neubaugasse 36/11
  1070 Vienna, Austria
  e-mail  helmut.schuetz.aaa.bebac.at
  web     http://bebac.at
  forum   http://forum.bebac.at
  
  

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• On 18 Sep 2007 at 22:08:49, "David Dubins" (ddubins.-a-.biopharmaservices.ca) sent the message
  

  
  The following message was posted to: PharmPK
  
  Hi Mathews,
  
  I developed a free tool in Excel to calculate sample sizes a little
  while
  ago. It's available here:
  
  http://individual.utoronto.ca/ddubins/FARTSSIE.zip
  
  I don't know where the 60% CV idea came from. Maybe it came from the
  fact
  that the total variance is the sum of the between- and within-subject
  variances:
  
  Sigma^2 = sigmab^2 + sigmaw^2
  
  As a worst-case scenario, if the intra-subject variance is assumed to be
  equal to the inter-subject variance, then the equation reduces to:
  
  Sigmaw = sqrt(sigma^2 / 2) = sigma / 1.212 = 70.7% sigma
  
  I've seen some people use 60% total CV, and others use 50%. In the
  end, you
  have to work with the data you have. If all else fails - run a pilot
  study
  to find the true ratios and variability of the test formulation. This
  provides the best sample size estimate.
  
  Hope this helps,
  
  Dave Dubins, B.A.Sc., Ph.D.
  Director Biopharmaceutics - Bio Pharma Services Inc.
  
  

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