- On 21 Jan 2014 at 10:06:23, claireong899.aaa.gmail.com sent the message

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Hi

If a patient taking drug A has a plasma level of X and a target level of Y is desired, an

incremental loading dose can be given. Assuming that the population volume of distribution of drug A

is V, in most PK textbooks to calculate the incremental loading it will be:

Incremental LD = [(Y-X)V]/S.F

where S is the salt factor and F is the bioavailability.

In the instance where there is enough information to calculate patient specific volume of

distribution (Vp), would it be wrong to calculate incremental loading dose based on patient specific

volume of distribution rather than using population V ?

ie Incremental LD = [(Y-X)Vp]/S.F

most textbook did not mentioned the use of patient specific population PK parameters?

thanks!

Claire - On 21 Jan 2014 at 12:51:53, Nick Holford (n.holford.-at-.auckland.ac.nz) sent the message

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Claire,

If you are making a prediction of an incremental loading dose for an individual then you should use

the individual (patient specific) estimate of the volume of distribution. This principle also

applies to other PK parameters such as clearance.

If your textbook does not mention patient specific parameters then I suggest you find a source that

discusses the target concentration strategy (e.g. see

http://holford.fmhs.auckland.ac.nz/docs/target-concentration-intervention.pdf slide 10 where revised

V and CL refer to patient specific estimates).

Best wishes,

Nick

--

Nick Holford, Professor Clinical Pharmacology

Dept Pharmacology & Clinical Pharmacology, Bldg 503 Room 302A

University of Auckland,85 Park Rd,Private Bag 92019,Auckland,New Zealand

email: n.holford.-a-.auckland.ac.nz

http://holford.fmhs.auckland.ac.nz/ - On 22 Jan 2014 at 08:49:47, Atish Salunke (atish_azad.-at-.yahoo.com) sent the message

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Dear Claire,

I assume now that your objective is incremental loading dose.

I was wondering whether incremental dose will be applicable or used for patient outside your study

and before doctor suggesst to increment the dose to a patient he/she calculate his/her volume of

distribution (V) and then decide the incremented dose then I am fine if you can calculate specific

volume of distribution (V) you should do the same this will be for your study only.

The mean of Sample volume of distribution (V) represent the volume of distribution (V) that you

would probably observe in population.

In case it is not feasible to calculate the volume of distribution (V) in each patient outside your

side when it comes to population where it would be actually used then you must use population volume

of distribution (V) to avoid bias.

Hope this help.

Regards,

Atish - On 22 Jan 2014 at 08:50:36, Prof. Dr. Zafar Iqbal (zafar_iqbal.-a-.upesh.edu.pk) sent the message

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Dear Claire,

I think it will be more appropriate if patient Vd is known

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