# PharmPK Discussion - Sample size for BE study

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• On 2 Jan 2010 at 14:26:44, Peh Kok-Khiang (kkpehken.at.gmail.com) sent the message
`The following message was posted to: PharmPKHappy New Year.I would be grateful if some one could assist me by explaining how tocalculate the sample size for BE study.I have conducted a preliminary bioavailabilty study for loratadine on6 healthy volunteers. From the study, I am able to calculate thevariance. How should I calculate the sample size ? What are the inputs? What equation to be used ?Appreciate for your reply. Thank you very much.Regards,PehLecturerSchool of Pharmaceutical Sciences,Universiti Sains Malaysia,11800 Penang,Malaysia`
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• On 4 Jan 2010 at 02:48:16, Helmut Schuetz (helmut.schuetz.-at-.bebac.at) sent the message
`The following message was posted to: PharmPKDear Peh,> [...] some one could assist me by explaining how to calculate the> sample size for BE study.>Well, based on the point estimate and CVintra (if your pilot was acrossover) or CVtotal (parallel).> I have conducted a preliminary bioavailabilty study for loratadine on> 6 healthy volunteers. From the study, I am able to calculate the> variance. How should I calculate the sample size? What are the inputs?> What equation to be used ?You cannot calculate the sample size directly (i.e., there's noformula). You only may calculate power (=1-beta) for a given combinationof acceptance range, alpha, CV, expected PE and given sample size. In aniterative procedure the sample size is increased until power >= desired(let's say 80%).See some posts (including links and code for free software) here:http://forum.bebac.at/mix.php?category=1Some R code here:http://forum.bebac.at/mix.php?category=19Your sample size was *very* low... So keep in mind, that *both* the PEas well as the CV are uncertain - not carved in stone. Don't get trappedby simply using these numbers as they are and feeding some software. ;-)It's possible to calculate an upper confidence interval of the CV basedon the Chi-distribution (but don't be shocked by the outcome for n=6).Also allow for a safety margin of the PE in the pivotal BE study.In the literature for loratadine CVintra of 30%-50% (Cmax) are reported,so be warned again not to rely on your pilot study's data *alone*. A lowCV value and a 'nice' PE may be pure chance.ICH E9http://www.ich.org/LOB/media/MEDIA485.pdfcalls for a sensitivity analysis in study planning.Best regards,Helmut-Ing. Helmut SchuetzBEBAC - Consultancy Services forBioequivalence and Bioavailability StudiesNeubaugasse 36/111070 Vienna, Austria`
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