- On 9 Jun 2006 at 11:02:44, "Laura T. Letendre" (letendrl.-at-.eden.rutgers.edu) sent the message

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The following message was posted to: PharmPK

Hi all,

I have two questions regarding bioequivalence studies:

1) WinNonlin outputs Westlake confidence intervals. When would it be

appropriate to use these confidence intervals and would they be

accepted by the FDA?

2) What is the correct way to do a sample size calculations for a

three way cross over study. I have 3 drugs to compare with 3

sequences. I am using nQuery advisory and I get a per group sample

size for a two group design. Is it correct to just multiply this

number by three - the sample size I am getting seems too high. Does

anyone have any references that would help with this?

Thank you in advance.

Laura - On 10 Jun 2006 at 10:30:39, "srinivas" (esreddy.at.bioserve.co.in) sent the message

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Dear laura,

Sample size calculation depends on coefficient of variation. If

coefficient

of variation is large, automatically sample size will come large.

You can calculate sample size using SAS software. In that you can get

sample

size N per group. So If study is three period, multiply N with three,

so you

can get sample size.

regards

Srinivasa Reddy.E

Research Analyst

Bioserve Clinical Research Pvt Ltd

Hyderabad. - On 13 Jun 2006 at 12:51:55, =?ISO-8859-1?Q?Helmut_Sch=FCtz?= (helmut.schuetz.-at-.bebac.at) sent the message

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The following message was posted to: PharmPK

Dear Laura!

>1) WinNonlin outputs Westlake confidence intervals. When would it be

>appropriate to use these confidence intervals and would they be

>accepted by the FDA?

>

Westlake's symetrical confidence interval is of historical interest

only and not accepted in any country...

IMHO they should be removed form WinNonlin...

>2) What is the correct way to do a sample size calculations for a

>three way cross over study. I have 3 drugs to compare with 3

>sequences. I am using nQuery advisory and I get a per group sample

>size for a two group design. Is it correct to just multiply this

>number by three - the sample size I am getting seems too high. Does

>anyone have any references that would help with this?

>

3 sequences are not adequate anyway; to compare 3 treatments you

should apply a 6-sequence William's design.

For details (including sample size estimation) look at this post

http://forum.bebac.at/forum_entry.php?id=50 and the followings.

best regards,

Helmut

--

Helmut Schuetz

BEBAC

Consultancy Services for Bioequivalence and Bioavailability Studies

Neubaugasse 36/11

1070 Vienna/Austria

tel/fax +43 1 2311746

Web http://BEBAC.at

BE/BA Forum http://forum.bebac.at

http://www.goldmark.org/netrants/no-word/attach.html

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