Computing Shelf Life with SigmaPlot



The SigmaPlot macro “Shelf Life” can be used to obtain an exact computation of a pharmaceutical shelf life time. No visual or numeric interpolation is required. A publication quality graph is created ready for submission to the FDA. The macro can be quickly rerun for multiple packaging and temperature/humidity data sets easily reducing the time required to prepare stability analysis input for a new drug application to a fraction of the original time.

Four different shelf life designs are provided one of which allows degradant analysis. Click on the link to access the setup program to install this macro.

A Typical Shelf Life Graph

The results of a typical shelf life analysis are shown in the following graph.

The drug activity data shown as solid circles has a linear regression line superimposed. The lower 95% confidence line is also graphed. The accepted definition of the shelf life time is the x axis coordinate for the intersection of the lower 95% confidence line with 90% drug activity (“Guideline for Submitting Documentation for the Stability of Human Drugs and Biologics,” Food and Drug Administration, DHHS, February, 1987).

This intersection is determined exactly by the macro – in this case 30.8 months. The numeric value is placed in the worksheet and shown on the graph by the dotted drop lines and the t90 = 30.8 label.

Using the Macro

If you are going to use this macro frequently then add it to a ribbon ( Creating a New Toolbox Ribbon Button and Adding a Macro Name To It ). Then enter time and activity data into the worksheet.

Run the Shelf Life Macro

Selecting the options shown here produces the graph above. But you can also select an Upper Specification design where the intersection of the upper 95% confidence line with an Upper Limit (%) specification determines the shelf life time.

The Lower and Upper design uses the minimum value of the two intersections. An example of this is shown in the left graph below. The shelf life time from a Degradant design for the Upper Limit (%) set to 5% is shown in the right graph.

Algorithm Validation

The algorithm has been validated using test data sets selected to span a spectrum of cases beyond those seen in practice.


SigmaPlot can be used to obtain an exact shelf life value and publication quality graph. Since no numeric interpolation is required, multiple data sets, saved in separate sections of a notebook, can be analyzed and graphed in a matter of minutes. Time is saved, accuracy is ensured and the graphs are ready for imbedding in a new drug application document.

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