Dear all,Back to the Top
has anyone experienced the case of a drug (ester) which rapidly hydrolyses
in buffer pH 7.4, but which is instead much stabler in 80% rat plasma
diluted with buffer pH 7.4 despite the presence of blood esterases? Sounds
wierd to me, but it is what I am facing at present. Would you suggest to
assay plasma protein binding of the drug?
No! it does not sound weird to me: let me propose the drug you have isBack to the Top
strongly bound within a hydrophobic pocket in the plasma protein and as
such cannot hydrolyze. You might want to try studying drug stability in
solutions of the drug in buffer/albumin and other plasma proteins. Vary
the quantity of protein to simulate plasma.
There is a drug I worked on some years ago, chlorambucil, which hydrolyzes
very quickly in buffer. In albumin buffer the hydroysis was markedly reduced.
Now chlorambucil is not an ester; it is a nitrogen mustard but conceptually
the reduction in hydrolysis could well be due to the same
interaction. Within the albumin domain chlorambucil is bound within a
"hydrophobic pocket" and as such is not available to water.
It would seem that protein binding is relevant to your directions
Angus McLean Ph.D.
BioPharm Global Inc.
8125 Langport Terrace,
Hello FedericaBack to the Top
I dont understand what 'much stabler in 80% rat plasma' means? I think the
hydrolyis is less in 80% plasma than buffer?
There are few suggestions,
1. try different buffer. If you are using PO4 buffer, try Tris
2. Try different PH
3.Try changing the incubation time.
4.Silanize the tubes.
We had the similar problem. More disappearance or hydrolysis of parent
compound (pyrethroid) in PO4 buffer, at slightly alkaline PH (8) and this
effect was time dependent i.e., hydrolysis was less if the compound was
incubated with buffer 30 min than 60 min.
It is highly likely that the liphophilic compounds stick to sides of
incubation tube or vials, because they don't want to stay in the
aqu solution. However, the situation is different in plasma because of the
presence of protein (enzyme??). We rinse the vials with 'Sigmacote'(from
sigma), to prevent this problem. The silanized tubes or vials are available
commercially also, if you want I can send the website.
Hope this helps
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