Expert: Dr.Paul Skett - 3/19/2008

Question
hello sir, my question is how does the conentration of drug in human plasma defined? i mean wheter the drug is present in water content of plasma or protein, exactly where?and how do i find an exact method to extarct it fully from plasma?i m working as a bio analyst in a CRO,hence want to knw hw to extract major amount of drug from human plasma for bio-equivalence studies on LC-MS/MS instruments,plz do reply??thank you.

Answer
Hi,

Unfortunately, there is no easy, single answer to this question as every drug differs!

Some drugs bind extensively to plasma proteins (warfarin binds 99%) whereas others have virtually no binding.

Extraction depends on the type of drug - there are different standard techniques for acidic, basic and neutral drugs - and, indeed, some drugs need specific extraction techniques.

It is important for you doing bioequivalence studies to know exactly the proportion of drug extracted but such controls are again specific for each drug and use specific marker compounds.

I am sorry I can't be more helpful here but, as I say, there is no single answer.

Best wishes,

Paul