Re: Different assays for different studies
Toufigh
If you treat BQLs as missing (rather than zeros), BQL observations in the older study should not interfere with the model. This would be similar to the project with several studies with different sampling schedules. Alternative is to treat BQLs using one of the more advanced methods (you can have different LLOQs for different studies in this case) but this involves using a more complicated code, Laplacian option, etc.: I would not do it unless you tried all other options and cannot get a good fit. If assays are different you may want to test assay effect on residual variability.
Leonid
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Leonid Gibiansky, Ph.D.
President, QuantPharm LLC
web: www.quantpharm.com
e-mail: LGibiansky at quantpharm.com
tel: (301) 767 5566
Quoted reply history
On 12/12/2011 2:24 PM, Toufigh Gordi wrote:
> Dear all,
>
> I am involved in a project, where data from several different studies
> are pooled and a PK model is being developed. The studies were conducted
> over a period of time and the bioanalytical assay was improved during
> this period. Hence, 2 of these studies have a LOQ of 1 ng/mL, while the
> others have a LOQ of 20 ng/mL. This results in all samples, including
> the very early ones, showing detectable levels of the compound for the 2
> studies, while the others indicate an apparent lag-time, since the older
> bioanalysis was not sensitive to detect the low concentrations at the
> beginning of the dosing.
>
> Any comments on how to deal with this situation?
>
> Toufigh
>
> Toufigh Gordi, PhD
> President, PK/PD and Clinical Pharmacology Services
> Rosa & Co. LLC: www.rosaandco.com http://www.tgordi.com/
> E-mail: [email protected] <mailto:[email protected]>
> Tel.: 408-480-7314
> Fax: 408-370-9810
>
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