Stability studies

Many of our clients come to us looking for new compounds intended for preliminary in vivo assays. The compounds must be administered to the selected animals in a controlled way, and sometimes a very simple but critical question arises: Are these compounds stable? We help our clients answer this question to increase the success of the assay.

The chemical stability of compounds in the administration medium is critical to the success of an in vivo assay. It is important not only to obtain the expected results, but to avoid a triple cost: the money invested in the preparation of the compound, money invested in the assay, and money invested in the animals, which sometimes require special characteristics and are extremely expensive. If a compound is not stable and decomposes before exerting its biological effect, the best-planned assay can be frustrated.

To avoid this, a good idea is to carry out a stability study of the selected compound under conditions resembling those the compound will find in biologic media. We present here a typical stability study carried out for one of our biotech clients.

Our client had requested the preparation of a compound in a quantity of less than a gram. The compound was intended for an assay with special rats and was to be administered as an aqueous solution in sterile water. The initial idea was to prepare the solution and stock it, replenishing the feeding bottles when needed. The obvious question before the assay could be carried out was the stability of the compound in solution during extended times.

To answer this question, a stability study was designed to know the effect of temperature (r.t. and 4 °C, the storage temperature) on the compound at different times. The purity of the compound before dissolution was taken as a purity reference value. The solutions were prepared, incubated at the indicated temperatures, and samples were taken and analyzed by LC-MS at given times.


Time 27 °C 4 °C

     0 h      97.28      97.28
     3 h      95.51      96.91
     24 h      88.22      94.86
     48 h

From the results obtained, it was clear that the compound was degrading quickly at room temperature. In fact, the purity was not even checked at 48 hours. The solution stored in the refrigerator at 4 °C showed better results, but not enough to be considered safe. In the end, it was decided that the compound, which was to be prepared at gram scale with higher purity, was appropriate for the assay, although smaller solution batches should be prepared and administered to the animals and the feeding bottles replenished at shorter intervals.