excessive urination and thirst

Question
I asked this previously but did not pose the question to accurately convey the problem.
A 4 month old male rat is urinating and drinking excessively - at least twice as much as the other rat.  Is this a problem with his kidneys and does he need medication or is this normal for some rats?

I mentioned that he was being treated for URI (upper respiratory infection) NOT an UTI (urinary tract infection).  Since he was taking doxycycline, I wanted to know if it might be causing this excessive thirst and urination.

What natural supplements might be of help to him?

Thank you for your response!

Answer
Unless he was born with kidney problems, it would be rare that he would had kidney problems this young.  As long as he is urinating as much as he is drinking, this is a good sign of healthy functioning kidneys.  Often with kidney disease, the rat may have an increase in water intake and a decrease in urine output showing the kidneys are not filtering properly.  

A urinary tract infection could cause urinary frequency, diabetes could cause excessive thirst, but this is  just grasping for straws and its not really fair of me to try to give you a diagnosis without having blood work drawn and a thorough exam by a qualified avian/exotic or a general DVM with a special interest in exotics and these vets.

As for the doxycycline, it can have an hepatic toxic effect on the liver but this is with long term use and I mean long term before there is any chemically driven liver damage due to use of this medication. It does not usually produce excessive thirst or increase urination as a side effect.

Perhaps he has been dehydrated and is simply making up for it? As long as he puts out as much urine as he is taking in of fluids, its a good sign.  Urinary frequency is a sign of urinary tract infection as well as signs of hematuria (blood in urine)

A urinalysis would not be a bad idea though and just in case you were going to ask if its possible he still can get a UTI while on doxy the answer is yes, since doxy is not really the drug of choice to use for this type of infection unless its from Gram-negative bacteria.
Trimethoprim sulfamethoxazole is the most widely used antibiotic for a UTI since it is a broad spectrum drug that destroys both gram positive and gram negative organisms.

As for natural supplements? It is said to use cranberry juice . It must be 100% pure cranberry juice so that it produces hippuric acid in the urine. This, in turn, acidifies the urine and prevents bacteria from sticking to the walls of the bladder. I cannot support this 100% though and prefer antibiotics to natural supplements, but that is how I was taught and I am not real up to par on natural supplements.  I wont knock it, I just dont know enough about it as we do not usually go this route in the clinical setting.

Anyhow, I would take him to the vet if you think he is doing something abnormal.  My rats are the same age and love water. All three guzzle water daily and I find I am refilling bottles every other day and there are two 8oz bottles in their cage.  

Does his urine smell strong?  Is it cloudy?

As for not giving the proper explanation to your question last time, I apologize. I must have mistaken UTI for URI.   My eyes must be getting old like the rest of me.