hi,Back to the Top
i have some confusion about the number of subjects to
be included in a BE study, i went thru the FDA site
but couldnt get over my confusion about the number of
subjects and syudy designs.
actually i want to design a 3 period study in which
two test fomulations will be tested against a
standard, would the minimum number of subjects i.e 12
give enough power to the study?
thanks
wajahat
Dear Wajahat,Back to the Top
For a BE study conducted according to a crossover design, the sample
size should be estimated based on the residual (i.e. intra-individual)
variability of the target parameter (generally Cmax and AUC). This
variability can be estimated from previous studies or sometimes found
in the litterature.
For a detailed overview and also tables of the required sample size in
a BE study with regards to the expected residual variability and to the
expected difference between the test and reference formulations, see:
Diletti E et al. (1991) Sample size determination for bioequivalence
assessment by means of confidence intervals. Int J Clin
Pharmacol;29;1-8.
For example: with twelve subjects, the power in demonstrating BE (Test/
Reference 90%CI within 0.80-1.25 assuming a multiplicative model)
reaches at least 80% only if the intra-individual CV is at most 15%.
Hope this helps ,
Fabrice Nollevaux
SGS Biopharma - Wavre - Belgium
www.sgsbiopharma.com
Dear Wajahat,Back to the Top
The sample size calculation depends on the power of the study and the
intrasubject variability of your drug. FDA recommends 24 volunteers for
2x2 crossover study. But you can use a larger sample size, based on
power and the intrasubject variability of the drug.
regards
Tausif Ahmed
Dept. of Pharmaceutical Medicine
Ranbaxy CPU, Hamdard University,
Delhi, India
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