Hi Mary,
We can figure out some actions of drugs based on their taste. Opioids like Hycodan taste bitter, which results in a descending action on Qi and Yang that, in moderation, can help relieve coughing which is due to the obstructed descent of Lung Qi. Cerenia has the same profoundly bitter taste and thus has a descending action of Stomach Qi. Both products, if used to excess, become excessively sedating due to their bitterness.
So, if we were to modify the herbs somehow in acknowledgement of the fact that extra descending action is needed, what would we try? Chai Hu Jia Long Gu Mu Li Tang encompasses Minor Bupleurum, but has added descending herbs. In theory, based on the need for those drugs, it should work better than Minor Bupleurum, so you could give that a try and see if the required dose of the two drugs to maintain the animal symptom-free is lowered.
Hopefully, that ends up being the case!
Steve