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calculating "Diss" from IVIVC


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#1 ARINDAM PAL

ARINDAM PAL

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Posted 12 December 2013 - 06:42 AM

Dear Sir/Ma'am

In one of the posts on IVIVC, from Simon Davis, I found that,

"'Diss' is an internal function that linearly interpolates the predicted dissolution data, i.e., the predicted data from the dissolution model that was fit to the In Vitro data."

 

I want to know where can I get the value of "Diss" in the ivivc file ?

How this internal function is calculated ?

 

I used the model Fabs=AbsScale*Diss(Tscale*Tvivo) for correlation, and got the AbsScale, Tscale values from correlation tab.

Manually, as a check, I tried to calculate the Fabs based on all the necessary parameters like AbsScale, Tscale, Tvivo but couldn't find the "Diss". Then, with Fabs, AbsScale, Tvivo & Tscale, I calculated the Diss from correlation eqn., surprisingly I found that value of "Diss" is changing with time parameters and is not constant.

Can you please help me out in finding ways to calculate Diss. I looked into the in vitro profile but couldn't find much.

 

Thank you

 

Regards

Arindam



#2 Linda Hughes

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Posted 12 December 2013 - 05:53 PM

Dear Arindam,

 

As Simon stated, Diss(t) indicates a function, the same as when you see f(t) used to represent a function f that is evaluated at a parameter t. Unless f(t) is a constant function, it will take on different values as the parameter t changes. Likewise Diss(Tscale*Tvivo) will take on different values as Tscale*Tvivo changes.

 

You cannot use Fabs, AbsScale, Tvivo and Tscale to calculate Diss, as you stated. You can only use Fabs and AbsScale to calculate Diss(Tscale*Tvivo), that is, the function Diss evaluated at the time Tscale*Tvivo.

 

When the Dissolution model for the In Vitro data is fit in IVIVC, the output contains Predicted Data which has columns for the times (vitroTimes), the predicted dissolution amounts, and the formulations. To compute the Diss function for an input time T, the Dissolution Predicted Data corresponding to the current formulation is used to either:

• find T in the vitroTimes if there is an exact match, and return the corresponding predicted dissolution,

• interpolate the predicted dissolutions corresponding to the vitroTimes surrounding T,

• return the first predicted dissolution if T is before the vitroTimes, or

• return the last predicted dissolution if T is after the vitroTimes.

 

When interpolating, simple linear interpolation is used. That is, to compute Diss for an input time T when T is between the vitroTimes t1 and t2, and y1 and y2 are the corresponding predicted dissolutions:

              Diss = y1 + ((T - t1)/(t2 - t1)) * (y2 - y1)

 

Regards,

Linda Hughes






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