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17 yr old cat hx: Hyperthyroidism unsuccessful unilateral thyroidectomy. Then had 1-131 rx 3 months ago. 3 lbs at lowest wt now 5.5lbs. Was 7 lbs in youthful prime. Now is HYPOthyroid at 0.2. Before any of above rx labs had elevated liver & NORMAL kidney. AFTER 1-131 I chose NOT to give recommended benazepril & one month post 1-131 bun & creat NORMAL except Hypothyroid. I then decided to start benazepril at half ordered dose to be safe according to body weight. I was giving 1.25mg daily not 2.5mg ordered. Now at 3 mos labs show an elevated bun 46 & creat 3.2. I read that in SOME cases, this could be due to the benazepril. I am choosing to stop this med and recheck labs in 1-2 months in case it is the med. I know about hyperthyroidism masking kidney failure etc... I know about the benefits of ace inhibitors in CRF. With her small size & the fact that 1 month POST 1-131 on NO meds bun/creat NORMAL. Could this med be a factor in elevated bun/creat? Want opinion on HYPOthyroid state also.

Submitted: 197 days and 8 hours ago.

Category: Cat

Value: $9

Status: CLOSED

Posted by Dr. Scarlett 197 days and 5 hours ago.

Answer

Hi,
Sometimes cats undergoing the I-131 treatment can have a low thyroid, at least for a period of time. As long as the cat is clinically normal--active, eating, feeling good, then no treatment is done (such as supplementing with thyroxine). Being hypothyroid certainly means decreased perfusion of the kidneys, which could cause them to function sub-normally and cause the increase in BUN and creat that is seen in your cat. So it might be worthwhile to try giving your cat a low dose of thyroxine and see what happens.

It is also possible to have a low T4 in a cat that is sick for some other reason--this is called "sick euthyroid" (euthyroid means normal thyroid). So maybe your cat has something else going on, such as kidney failure that, coincidentally, showed up at this time. It is certainly a common problem in old cats and may have been slowly coming about before the I-131 treatment. Do you know what your cat's urine specific gravity was prior to the treatment?

As far as the benazepril-was it prescribed because your cat had some protein in the urine? (Has a urinalysis been done recently?) Or was it just a preventative thing? For a heart condition (hypertrophic cardiomyopathy)? High blood pressure? It would help me answer your question if I had a better idea why it was prescribed.

Thanks,
XX. XXXXXXXX

Let me know and I'll

197 days and 5 hours ago.

Reply

The specific gravity prior to 1-131 was borderline dilute and I don't have that particular #. The dr stated the cat was probably in a stage 1 kidney disease according to the specific gravity even though bun/creat ok. This med was considered preventative since they were proceeding with 1-131 and lowering thyroid. It was not prescribed for hypertension or myopathy etc...
Since that initial urine there was a specific gravity obtained 1 month post 1-131 which was 1.015 and the most recent 3 months post 1-131 which was 1.013. I think the vet mentioned with this most recent urine there was some protein but that had not been the case before from my understanding. So, would it be reasonable in your opinion to stop this med and see if there is a change in labs? Since she had only one thyroid gland left before 1-131 it seems possible she had more diseased thyroid that was destroyed and not much good left to produce the hormone. How would you proceed if this were your cat?

Accepted Answer

Hi,
Based on the specific gravities your cat definitely had signs of renal failure prior to the I-131. So I'm not terribly surprised at the increased BUN and creat. Since the benazapril wasn't prescribed for a specific reason (just having some protein in the urine really isn't cause--you need to document that it is significant protein based on a urine protein:creatinine ratio and make sure there is no infection), I would definitely stop the drug. I would also recommend having a blood pressure taken to make sure your cat isn't hypertensive. High blood pressure can also impact the kidneys.

I wouldn't necessarily give her any thyroid medication, unless she was acting sluggish (ok, a little hard to tell in a 17 year old cat), not interacting with you as she normally does, etc. But it probably wouldn't hurt to try her on a low dose of thyroxine if you do think she is lethargic.

Good luck!
Dr. Scarlett

Accepts:
Expert:	Dr. Scarlett
Pos. Feedback:	100.0 %
Answered:	5/10/2009

Cat Veterinarian

I am a practicing small animal veterinarian with 13 years experience.

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