2-Year Old Mini Dachshund - Kidney Failure? Need any guidance.

Age: 2.2 years old Sex/Neuter status: Female/Spayed Breed: Mini Dapple Dachshund Body weight: 12.4 lbs History: Our dog, Winnie, began acting lethargic and didn't seem to want to use her stairs to get on the couch, etc. She was also eating very little of her kibble (Science Diet - Small Breed). We took her to the vet, who did an exam, and determined she may have a slight bruising in her back near her head (no clue what this would be from - she is really a home dog in an apartment). They prescribed Rimadyl and Trazadone to see if alleviating pain would make her eat and be more comfortable. She seemed to bounce back a bit and eat on the medicine, but then she really slowed down again. Her behavior was normal at times. She started urinating a lot (clear) and slowing down eating again. Chicken and rice changed that for a bit, but slowed again. Took her to vet yesterday (total of 3 weeks since beginning vet visit), and her blood test showed elevated BUM levels (127). Told us to take her to the ER as would take them days for tests to come back. Clinical signs: Elevated blood work from kidney function. BUN of 127. Duration: 2.5-3 weeks Basically, I am terrified from reading about these results. We cannot think of a single thing she would have ingested that would cause toxic impacts to her body like this. My girlfriend is recovering from a bad surgery and is home all day long with the dog, except leaving here and there for a few hours. Is there any way the prescription medications given for her back pain caused this big of an impact on her kidneys? I am so confused. They kept her at the ER/Internal Medicine overnight. Gave them a $5k deposit and asked what the plan was. They are going to do an ultrasound on her abdomen this afternoon. Skeptical side of me thinks the end result is going to be the same no matter what after reading about dog kidney failure. I can get more blood test results when I get home. I just want to know if I am going down the right path or if there is something else I should be doing to save her life. She is acting healthy for the most part, but all of the signs - urinating clear most of the day, bad breathe (more than normal), lethargic, and just not being her old self - point to something I fear is bad and the worst is I don't know what happened. If she ate a big bowl of grapes or something I'd understand, but this came out of nowhere (and I guess the WHY doesn't matter now). Yesterday, after doing some research, we asked the ER if they are running the chance she has lepto, which they replied they are treating her as if she does until those test results come back. She has been on fluids all night and is doing well from a critical care standpoint (is stable). They will do another blood test in 24 hours as that is how long you have to wait. They did an ultrasound on her abdomen, kidneys and said the kidneys are slightly enlarged, which is more promising than a congenital issue if that were to be the case. Today, there has been no real news as of yet. At about $1000/day in this ER just waiting for tests, I hope I am doing the right thing.

Sorry for the formatting. Looks like it all went away when I posted so it is just a jumbled post.

Hello!  An elevated BUN can be very concerning, although it is usually considered with some other factors, the specific gravity (ability to concentrate urine) and creatinine (alongside BUN).  I have seen dogs with a very high BUN for a short space of time recover well (it can, for example, be increased because of dehydration), but that doesn't sound like the picture here.  My judgement on this case is worth nothing: I don't have the full picture and nor am I your vet. I think the question you should be asking your vet is:  What are the chances of the kidney function returning?  What would they do in your position they had X more dollars to spend?   Have they even seen a dog in this position get better?  Would a kidney transplant be needed? I guess the 24 hours are up now so you may have the answers you need.  It sounds like a tough time for all of you - best of luck.

*ever* not *even*

How went the next blood test?  This is a nail biting time for you. You have already mentioned toxins and leptospirosis; other causes of such dramatic kidney changes may include heatstroke or potentially the bites of some kinds of snake (might this also explain an odd stiffness?)  Indeed, an overdose or adverse reaction to some kinds of drug should be on the list - your vet will probably have access to the toxicology information about the meds that they gave. Thinking of you and Winnie.