Julie,
I am still studying TCVM but do work with experience herbalists.
I guess my mentors would ask by saying what are the reasons for the two formulas used (apologies if there was a previous thread with rationale explained)
Also ensure he doesnt have any sequalae including UTI/ crystalluria.
Is there any other differences between the litter mates, heat/cold intolerance, historical gastrointestinal disease issues etc.
Is she on any other herbs, supplementation, diet modifications for other issues that may be further supporting kidneys by default, i.e. probiotics for gut problems re: microbiota difference on renal function.
Do you have a western biomedical dx for the cause of kidney disease? if it is cystic perhaps he has larger cysts?
Depending on signalment, and dog is clinically well, perhaps an SDMA of 16 and Creat < 200 may be ok with ongoing support to support remaining nephrons/ slow fibrosis.
Do you have a UPCR?
Matt