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  • 1.  Mean Residence Time (MRT)

    This message was posted by a user wishing to remain anonymous
    Posted 09-21-2025 19:15
    This message was posted by a user wishing to remain anonymous

    Hi All,

    What is the significance of mean residence time? I compared elimination half life (t1/2) of a few compounds with MRT. In many cases (case 1), MRT was higher than t1/2, but in some cases (case 2) MRT was similar to t1/2. Can we conclude anything from these 2 cases? 

    Thanks in advance!



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  • 2.  RE: Mean Residence Time (MRT)

    Posted 09-22-2025 10:06

    Dear,

    the MRT can be  considered the avearge time a molecule stays in the body. However, since it's a result of calculation where moments are applied, it's a statistical parqmeter, 

    t1/2 = ln(2) * MRT

    Pharmacokinetic moment theory borrows from physics/statistics:

     - The 0th moment of a function (∫C dt) corresponds to AUC.
    - The 1st moment (∫t·C dt) corresponds to AUMC.
    Their ratio (AUMC/AUC) = the mean time (MRT) that drug molecules spend in the body.

    Really by numerical comparison in a single compartment for IV bolus is:

    MRT = 1/lke

    Whers lke is the the exponent of first order elimination C= exp(-ke x t).

    TYhen in the simples 1 compartment elimination (without any absorption) you will have t/2 =  ln(2) x MRT

    the MRT is always higher then t/2 

    Often ke is called lambdaZ.

    Best

    Stefano



    ------------------------------
    Stefano Porzio
    CMC and Development Director
    Enthera Srl
    Milano
    [[email protected]]

    Disclaimer: Opinions expressed are solely my own and do not express the views or opinions of my [email protected]
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    Original Message


  • 3.  RE: Mean Residence Time (MRT)

    Posted 09-22-2025 10:34

    Dear,

    I apologize for typos.

    About the difference between 2 MRTs: usually difference is possibly related to the analytics and to the calculations, I mean regression for ke and moment calculation for MRT).

    Only as example for a first compartmental IV bolus: if you have an analytical method and sampling allowing excellent description of elimination phase, than MRTz (MRT calculated by using terminal half-life) follow exactly the relation t1/2 = ln(2) * MRT, but if you cannot describe a "realistic" elimination phase then you will not have a "credible" half-life, MRT will describe better the time spent in the body since it's obtained by the area under the 1st moment curve and area under 2nd the moment curve, and t1/2 cannot be considered a good parameter.

    Anyway, when you have more complex kinetics, I mean more than 1 compartment, complex absorption and distribution, etc., MRT takes in account all the curve (really for an absorption you can try to obtain also MIT, the mean input time, i.e. the mean time for input simply as MIT= MRT-MRTz, where MRTz is the elimination MRT calculated as 1/ke).

    In conclusion, for simplest kinetics, some level of comparison between MRT and t1/2 has a meaning, but for more complex profiles and kinetics, the direct comparison is not possible.

    Anyway, the MRT calculated as AUMC/AUC can be easily always used for comparative pourposes without any hypothesis on compartments.

    Best

    Stefano



    ------------------------------
    Stefano Porzio
    CMC and Development Director
    Enthera Srl
    Milano
    [[email protected]]

    Disclaimer: Opinions expressed are solely my own and do not express the views or opinions of my [email protected]
    ------------------------------

    Original Message


  • 4.  RE: Mean Residence Time (MRT)

    Community Leadership
    Posted 09-26-2025 01:37

    As Stefano noted, MRT is the average time molecules reside in the body, so it's common for MRT > t½. If you see MRT ~ t½, I'd first look for BLQ-truncated terminal points that could be skewing the tail (and the t½).

    MRT reflects average residency (not just the terminal slope), two molecules with similar t½ can still have different MRT, which I find useful for formulation calls and spotting flip-flop absorption. 



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    Pankajini Mallick Ph.D.
    Sr. Principal Scientist, DMPK, PK/PD
    San Diego CA


    Disclaimer: Opinions expressed are solely my own and do not express the views or opinions of my employer.
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    Original Message