This particular curve fit aims to model a process following exponential decay. Exponential decay is defined as the process of reducing an amount by a consistent percentage rate over a period of time. If you are interested in modeling exponential decay data sets in the context of IV dosing or PO dosing pharmacokinetics, please see this article.
To implement the exponential decay curve fit, users can follow these steps:
- Creating readouts for input data such as timepoint and plasma concentration
- Creating a plot type readout to generate the curve fit
- Data calculations for different intercepts (optional)
- Editing and saving the curve
Lets work through an example where we will implement this curve fit within our “Microsomal stability” protocol.
Create a numerical readout for the X-axis values:
Create a numerical readout for the Y-axis values:
Create a readout to plot the curve and calculate any optional intercept values:
Pro tip: Create conditional readouts for parameters such as cell line or concentration of drug. Also, consider plotting custom calculated readout values on the Y-axis such as % remaining substrate within the context of this microsomal stability example.
Our protocol now captures our input data and automatically generates an exponential decay curve for each entity per run of the protocol. As shown below, be sure to customize your report to include the relevant calculated readouts such as the decay rate constant, K, or the area under the curve. Please see below for a full list of auto-calculated parameters.
Fit Parameters:
The Exponential Decay curve fit is performed using the following equation:
Where
Y= The dependent readout value at value, x
C0= The initial dependent readout value at x=0
Cmin= The minimum dependent readout value- the non zero asymptote
K= The rate constant
x= the independent variable
The following parameters will automatically be calculated by CDD Vault for this plot type:
- AUC - observed
- C0
- Rate constant, K
- Cmax
- Cmin
- N
- Plateau
- R-squared
- Span
- Tau
Area under the curve:
- The CDD Vault AUC is calculated as the (positive area - negative area) under the curve where:
- The curve is defined as straight line connections between responses, not the fitted curve (Linear Trapezoidal Non-uniform grid method)
- Units are response units*dose units
- The baseline is set at the negative control mean or 0 if control data is not available
Additional calculations:
Please note that all auto-calculated parameters listed above can be used in custom calculations as separate readouts. These parameters can be accessed within our robust formula editor.