Hi Sarah,

Her serum potassium levels should be monitored *very* closely because she's
also taking a potent ACE inhibitor.  Your vet should be aware of this drug
interaction  - but if I were you, I'd err on the side of caution and bring
it to his attention *immediately* just in case it slipped his mind.

If her body stores of potassium were depleted, the supplement will make her
start feeling and acting and even looking better, and her appetite and
haircoat should also improve.  Since there isn't a simple, routine test to
monitor body potassium depletion, all you can do is monitor her serum
potassium levels to avert life-threatening hyperkalemia and see if she
starts acting and feeling better after receiving the supplement for about a
month.

Earlier you mentioned she was diagnosed with CRF but now her BUN/Cr are
normal.  ACE inhibitors have been known to slow the rate of progression of
CRF in cats and also increase whole kidney GFR.  An increase in GRF would
certainly lower her BUN/Cr.

Another possible explanation for her improved kidney function could the
development of mild hyperthyroidism.  The next time you take her to the vet,
ask him to test her thyroid function.  Because she may have something else
going on, I would tell your vet to have her thyroid function assessed with
the Free T4 by Equilibrium Dialysis assay along with the routine free T4.
Both blood samples should be sent to the lab together.

Keep the faith!

Phil.