I think both plasma and serum are acceptable. Which one is better depends on your drug studied. If the concentrations of your drug in blood are rather low and you don't have a very sensitive method to detect them, plasma would be a better choice, considering the higher drug recovery rate from blood and larger volume than serum. On the other hand, the less protein concentration of serum lowers the demands for sample pretreatment.

Does this mean that one gets cleaner sample from serum as compared to plasma ? Will appreciate if you can cite any published reference as I tried but all in vain.

as Yufeng said, it depends on your drug, do you know if it is highly-protein bound? you don't want a 'cleaner' sample that has a non-representative measurement of your drug!

It depends on the drug or metabolite you want to measure. Both the Youfeng and Simons answers are adequate. Usually for expected low concentrations plasma is more appropriate. An effective extraction method must be used especially in the case the substance you are measuring is highly-protein bound....

Thank you for your inputs.

Most probably all clinical samples were measured with serum, but for the animal models usually they will go for plasma due to low sample size.

I think that the two attachements can get you a clear Idea

Dear Anand, thanks for your inputs. Since I am working with herbal extracts, I feel it makes more sense to work with plasma as it will not cause a considerable loss of analyte as plasma bound. Please correct me if am wrong.

Rohitash

Ya, for herbal extracts you can go for plasma instead of serum, because all the active ingredients will be present , if it reaches the circulation.

It can also depend on what species you are performing your PK studies in and the logistics of sampling. Large species such as man and dog there is the luxury of large sample volumes. However, with mice for example one must consider any contribution of the volume of anticoagulant used (or use dried anticoagulant) to collect small volumes of blood in order to obtain plasma.

Andrew, thanks for your input.

We generally use plasma. We careful that you don't loose compound when using serum.

Dear Dr. Hochhaus

Thank you for your suggestion. With my personal experience I have noticed that there is a considerable loss of compound (in case of herbal drugs) when I chose serum over plasma. I don't have a specific reason as to why this happens but I suspect fibrinogen as the reason (removal of fibrinogen bound compounds).

We generally use plasma.

Dear Rohitash,

Sorry for late reply...!!!!

But as per my understanding about Pharmacy and Ayurveda, I would like request you if you can please go for both (initially may be using pilot study) serum and plasma. Since herbal formulations contains many constituents which we know and which are yet to be known. So the entire formulations together plays role in Vol. of distribution , PPB, and all other parameters of PK-PD.

Please let me know your opinions/experience about the the same.

Thanks

Best regards

Swapnil

The pharmacokinetics of a given drug may vary depending on the sample type. Also, the metabolic components of plasma and serum are considered to be different. I would therefore suggest to use both serum and plasma and make a comparison if resource is not a limitation. That would be interesting and it strengthens your findings.

Check Yu et al 2011. Plos One Paper.  Differences between Human plasma and blood metabolite profiles. 

........human plasma and serum metabolite profiles.