I have the invitro and cell based invitro concentration of a molecule . But I am struggling with deciding the concentrations that should be screened in mice for the pharmacokinetic study of the molecule. How can we extrapolate the invitro data for setting up invivo experiments?
Dear Tejosmita Sen
Few points should be useful I hope:
- develop bioanalytical method for your molecule determination in blood plasma (or blood plasma and whole blood after hemolysis) without a method you cant do your PK study. Moreover you cant make next steps.
- check ex vivo using blank full blood cell fraction and blood plasma, or hemolysed full blood (frozen blood) does your molecule transfer to RBC or not (then you will know what analytical matrix will be useful for you.)
- Calculate LogP of your molecule. If its lipophilic structure with LogP more less >1 then please remember how big impact it could have for binding with plasma proteins (recovery of your analytical method), affinity for other proteins for example with enzyme activity (CYP) (first pass effect possible).
- decide about route of administration and local toxicity (local toxicity should be a part other tox studies) If IV is possible its easier route for you, if not IP could be usefull. Please remember after IV take first samples immediately after drug administration for example 30 sec, after drug administration 2 min 5 min 15 min 30 min ...... its most important samples because show close to t0 observed concentrations which can go dawn with very high rate.
- use tox studies for planning dose which could be well tolerated
- check carefully what is available in relation to monologues (NCBI etc.)
- make pilot study using 3 animals and for example three doses. Example 1mg/kg (one animal), 3 mg/kg (one animal), 9 mg/kg (one animal). If its IV from fist take sample after 30 sec, from next after 30 sec and from last after 3 hours. Analyse data and trends for first PK study sampling optimization.
- With first PK mice study my suggestion is applying sparse sampling. and two stage approach if sampling will be to short to cover whole PK.
Best regards
Tomasz
Dear Tejosmita Sen
Your question is very important and in my point of view that it is not easy to correlate the invitro doses with invivo doses because when you have a cell culture for a cancer for example and calculate the IC50 value , it doesn't mean that this dose will give you the expected response. You have to consider the PK of the molecule, tissue distribution , extent of metabolism either in organs or in blood sample, PK difference in diseased subject is completely different than healthy one. So as previous comment by Dr. Tomasz, you have to validate a bioanalytical method first before settle on a definite dose under study ,, Best wishes
Hi Tejosmita,
if the compound has known pharmacokinetics (PK) model (ADME) in mice, then you can calculate the oral equivalent dose equivalent of the in-vitro concentration . For example, let say you would want to see the effect of compound in the liver (target organ) toxicity or pharmacological response, then you can use following three methods: 1) calculate the in-vitro AUC, which is equivalent to in-vitro dose multiply by time of exposure, and use this AUC as a target organ AUC. Then titrate oral dose in PK model till you get the desired target AUC (equivalent of in-vitro). 2) assume in-vitro concentration as a steady-state concentrations in blood or target organ and then titrate the dose till you get the in-vitro equivalent in-vivo Css. 3) you can assume the in-vitro concentration equivalent to cmax (taget organ), then apply the same method to PK i.e. titrate the oral dose till you observe the in-vitro equivalent in-vivo Cmax. This method called as Quantitative in-vitro in-vivo extrapolation (QIVIVE) method.
Here are few references that would help you:
Article In vitro-to-in vivo extrapolation (IVIVE) by PBTK modeling f...
Article Developing Integrated PBPK/PD Coupled mechanistic pathway mo...
Article Quantitative in vitro-to-in vivo extrapolation (QIVIVE) of e...
Best Wishes,
Raju
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