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At-home testing for presence of GS-441524, EIDD-2801, and GC376

At present, a large and entirely unregulated market for antiviral products to treat feline infectious peritonis (FIP) exists.  While many cat owners have reported success with these products, the quality and accuracy of the labeling of these products is of great concern.  Issues could include more or less active ingredient than labeled, low purity, contamination, or substitution of the active drug.

There is a relatively simple test which can be done at home with products easily purchased online which can help differentiate between some of these antiviral drugs.  This test was developed by Megan Browning from the University of Utah and will be part of an upcoming paper to be published in a peer-reviewed journal. (Currently available  in preprint here.)

Please note, this test is not a substitute for rigorous, independent lab testing, however it may be of use in quickly identifying products of concern.



Links are provided for the items shown and used in this demonstration

TLC plates

95% or higher isopropyl alcohol or ethanol

A 254 nm UV Lamp

A graphite pencil

A fine tipped tool to apply sample

A glass jar for developing samples


Preparing Samples

  • If necessary, the TLC plate can be cut to fit the developing jar

  • Label samples at the bottom of the plate

  • Apply a very small amount of sample to the plate using the fine-tipped tool.  Allow to dry.


Differences can often be visualized under a UV lamp at this stage, with no development necessary. GS-441524 glows blue. Molnupiravir looks like a black spot, and GC376 barely absorbs and is nearly invisible.


Developing Samples

  • Put a small amount of ethanol in the bottom of the jar, such that the liquid level is lower than the line drawn on the plate. Close and shake.

  • Open the jar and put the TLC plate in sample side down, taking care not to get the sample spots wet.

  • Replace the cover or cap for the jar

  • When the liquid levels near the top of the plate, remove the plate and let dry.


Visualizing Results

Using the UV lamp, visualize the results.

The image on the left shows samples containing (from left to right)  GS-441524, GC376, and EIDD-2801.

The image on the right shows samples containing (from left to right): GS-441524, a mix of both GS-441524 and EIDD-2801, and EIDD-2801

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