I'm so sorry to hear that. I noticed this in the sidebar and had to come say something. My mum and I keep pet rats, and while the health problems in Australia aren't quite as pronounced as in the US, the average lifespan for a rat is still about the same, no matter what we try.
 
It sounds like he has advanced mycoplasma causing respiratory problems, which is the biggest problem we have here, too. It's nearly impossible to find a rat which doesn't have that issue born into them from the moment they come into the world, and those who dodge the hereditary bullet just end up catching it off other rats. It quickly grows resistant to most antibiotics and is the nastiest, most widespread disease plaguing any domesticated pet species ever, I'd think.
 
Just a few tips which make help him perk up; I found letting my rats run around in the bathroom while I'm taking a hot shower really helps, as the steam loosens the mucus buildup in their lungs. If he's never had antibiotics before, medicines like Baytril (Enrofloxacin) and Vibravet (Doxycycline) may give him a new lease on life for a while. But mostly, just keep him comfortable and show him heaps of love. He's a real cute old guy.

I'm so sorry to hear that. I noticed this in the sidebar and had to come say something. My mum and I keep pet rats, and while the health problems in Australia aren't quite as pronounced as in the US, the average lifespan for a rat is still about the same, no matter what we try.

 

It sounds like he has advanced mycoplasma causing respiratory problems, which is the biggest problem we have here, too. It's nearly impossible to find a rat which doesn't have that issue born into them from the moment they come into the world, and those who dodge the hereditary bullet just end up catching it off other rats. It quickly grows resistant to most antibiotics and is the nastiest, most widespread disease plaguing any domesticated pet species ever, I'd think.

 

Just a few tips which make help him perk up; I found letting my rats run around in the bathroom while I'm taking a hot shower really helps, as the steam loosens the mucus buildup in their lungs. If he's never had antibiotics before, medicines like Baytril (Enrofloxacin) and Vibravet (Doxycycline) may give him a new lease on life for a while. But mostly, just keep him comfortable and show him heaps of love. He's a real cute old guy.

Sadly I'm well aware of mycoplasma, it claimed my 2nd rat I owned when I first got Gizmo, it turned into advanced phenmonia and we did all we could including nebulization therapy, which is the same as your hot shower idea only it litterally steamed antiboitics. I do still have the machine and could actually give him steam therapy but being kept in that box for a time stresses them out and really doesn't do much at the end.

He's been on antibiotics for awhile with no change, (and yes its the same antibiotics you suggested, I use it all the time for my ratties) but sadly he's not changed much nor really improved. So at this point im just keeping him comfortable.

I'm deeply sorry to hear this, Blissy. Gizmo looks absolutely adorable. The thought of losing a pet like him is heart-wrenching. You have my sincerest condolences *cuddles*

I had rats growing up, though my current horde of pets is missing one. They're some of the best pets one could ever ask for, aside from their short life span. Give Gizmo the best life you can, and remember him well when he's gone.