Modeling of dissolution profiles

Question

Dear all,

How to fit kinetic models to dissolution profiles? The most common for pharma are referred to below. I tried the non-linear modeling with the weibull function and the linear (zero-order), but the rest is not available. Does anyone have a functioning script or a solution for this?

Many thanks in advance!

Marta

Mark_Bailey · Accepted Answer

The nonlinear regression in Fit Curve and Nonlinear both require starting values. Fit Curve uses heuristics associated with each model to obtain starting values from the data. Nonlinear does not have this feature. You must specify the starting values when you define the parameters in the Formula Editor.

The heuristics simply consider the interpretation of the parameter and estimate the starting value. For example, a parameter might represent the central tendency of the curve, so the mean or median are good choices. Or another formula might have an inflection point, so the mid-point might be a good choice.

The regression then searches for estimates (minimizes loss function) until any of the convergence criteria are met. It is not a closed-form exact solution.

Yes, some functions are particularly difficult and demand more careful selection of the starting values.

marta-simoes · Accepted Answer

Thanks Mark! It is clear now!

I was able to put all the equations working with some adjustments in those parameters.

Thanks for your help!

Marta